Deductions & credits

Based on what you included in your post, it appears the coins were personal property and not investment property.  As such, any gains from the sale of the coins would be considered a capital gain and reported on your tax return.  Any losses realized in connection with the sale of personal property are not deductible.  You would still report the sale even though it resulted in a loss; however, when you report the sale you can report the cost and the sales proceed amounts as the same resulting in no gain but also no loss.  

You indicated that you do not remember your cost basis because the coins were purchased many years ago.  Assuming you have exhausted all reasonable research methods, (numismatic experts, coin clubs, etc.) you might consider just using the face value of the coins as a basis.  To avoid unreasonable speculation, presumably when you purchased the coins, the seller sold them at their face value plus a mark-up.   However, given the passage of time, and the unique character of the items at issue, it will be difficult to determine your cost basis and therefore, you will need to do the best you can to arrive at a reasonable cost basis. 

Sales of this type are entered in the Investment and Savings section of TurboTax.  As the coins are a capital asset, their sale information will appear on Form 8949, Sales and Other Dispositions of Capital Assets, and Schedule D.  Here are the steps to follow to enter your coin sales if you are using TurboTax online.

1. Sign-in to your account.
2. Select Federal in the left margin.
3. Select Wages & Income, left margin.
4. On Your Income and expenses screen scroll down to Investment and Savings.
5. Click on the drop-down arrow if necessary to reveal more options.
6. Click Start/Revisit across from Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B).
7. At the screen Let's import your tax info, you will see the option to Enter a different way.
8. Then select the type of investment.  For you it will probably be Other.
9. Continue to enter information as prompted.
10. At the screen Now, choose how to enter your sales, make the appropriate selection.
11. Enter your coin information. 

Did you sell any of these coins through an online portal/processor, such as eBay, Amazon, etc.?  If so, did you receive a 1099-K?  Please follow-up with this information if applicable.  

@RockinRonaldo