The decision on whether to spend or save coins is usually pretty simple. In nearly all cases, if you don’t spend them, then they’re just a pile of metal gathering dust. But there are rare instances when that pile of metal might hold a fortune, such as a Sacagawea Dollar coin worth six figures or a Lincoln penny worth a couple million dollars.

For You: 4 Lesser-Known Coins That Are Worth Thousands of Dollars

Learn More: 7 Tax Loopholes the Rich Use To Pay Less and Build More Wealth

Lincoln pennies are well known — chances are you have a bunch of them taking up space somewhere in your home or car. Sacagawea Dollars are not nearly as well known, but they are beloved by many coin collectors. With that in mind, let’s dive into some Sacagaweas — and other coins — that might be worth holding onto.

The U.S. Mint started issuing the Sacagawea Dollar in 2000 in honor of Sacagawea, the Shoshone Native American who as a teenager helped guide Lewis and Clark on their famous westward expedition. The dollar coin was issued near the 200th anniversary of the expedition, which occurred from 1804 to 1806, according to the National Archives website.

In addition to its fetching design, the Sacagawea Dollar has appeal for its historical significance as well as the fact that it’s still one of the few U.S. coins to feature a real woman instead of a fictional one (another example is the Susan B. Anthony Dollar). Compared with other coins, the Sacagawea Dollar has a low circulation, adding to its appeal.

As with any coin, the value of a Sacagawea Dollar depends on its condition and its rarity. Most of the coins you find will be worth about face value, though you can usually get a few cents more than $1 because they are so prized.

Read Next: Do You Have a $2K Quarter? Look Closely Before You Spend This 2004 Coin

But there are a few error varieties that fetch tens of thousands of dollars. Here are the five most valuable versions:

1. 2000-P Sacagawea Dollar and statehood quarter mule ($144,000): In coin terminology, a “mule” refers to two different designs on a single piece. In the case of this Sacagawea Dollar, one side is stamped with George Washington’s head and the design for a quarter, while the other side features the back of a Sacagawea Dollar with a soaring eagle design. There are only 18 known examples of this minting error. One of them sold at auction in 2022 for $144,000.

2. 2014-D Sacagawea Dollar and presidential dollar mule ($84,000): Another error coin that has a Sacagawea Dollar on the front and a presidential dollar on the back.

3. 2000-D Sacagawea Dollar and South Carolina quarter mule ($66,000): This error occurred at the Denver Mint in 2000 when the front of a Sacagawea Dollar was paired with the back of a South Carolina statehood quarter, according to Love to Know. It took more than two decades for this coin to be discovered, and it sold in 2022 for $66,000.

4. 2000 Lincoln cent on Sacagawea Dollar ($35,000): Another mule coin, this one features a Lincoln cent stamped on top of a Sacagawea Dollar.

5. 2000-P Cheerios Sacagawea Dollar ($34,500): This very rare version first came out in 2000 when the Cheerios cereal brand and the U.S. Mint ran a promotion in which the coin was placed in a few boxes of cereal. Finding one in mint condition can make you tens of thousands of dollars richer.

Your chances of running across one of the rare and highly valuable Sacagawea Dollars are slim — which is why they are so valuable to begin with.  The same holds true for any coin, whether it’s a 50-cent piece, dollar, dime, nickel or penny. The vast majority are only worth face value, which means there’s no reason not to spend them.

If you are on the hunt for valuable versions, the Hero Bullion site recommends looking at these factors:

• Age and rarity

• Condition and mint mark

• Precious metal content

• Historical significance

• Collector demand

Oh, and about that $2 million Lincoln penny mentioned earlier: It would have to be 1943 Lincoln Head Copper Penny, produced during World War II. During this period, the U.S. needed all copper and nickel to go toward war efforts, so most of the pennies were made with steel, according to the Luxe Digital site. However, one batch was mistakenly made with copper.

Only 20 to 40 copper varieties are believed to be in existence today, and most range in value from $100,000 to $500,000. But a rare 1943-D graded PCGS MS64 Brown version sold for $1.75 million in 2010, which Luxe Digital estimates would be $2,325,200 today.

More From GOBankingRates

• Surprising Items People Are Stocking Up On Before Tariff Pains Hit: Is It Smart?

• 12 SUVs With the Most Reliable Engines

• 5 Little-Known Ways to Make Summer Travel More Affordable

• 6 Popular SUVs That Aren't Worth the Cost -- and 6 Affordable Alternatives

This article originally appeared on GOBankingRates.com: Spend or Save? Why Sacagawea Dollars, Half Dollars & Other Interesting Coins Might Be Worth Keeping