There is a difference between coins and bars; coins are collectibles while bars are not and the capital gains tax rate on collectibles is 28%.
See https://www.irs.gov/taxtopics/tc409
In TurboTax, you would enter the sale in the Stocks, Mutual Funds, Bonds, Other subsection of the Investment Income section.
Note that you cannot deduct a loss on the sale of collectibles (such as coins) that you held for personal use.
