Monetary Metals Tax Neutrality Act of 2018 This bill amends the Internal Revenue Code to exempt gains or losses from the sale or exchange of certain coins or bullion from recognition for income tax purposes. The exemption applies to gains or losses from the sale or exchange of: (1) gold, silver, platinum, or palladium coins minted and issued by the Department of the Treasury; or (2) refined gold or silver bullion, coins, bars, rounds, or ingots which are valued primarily based on their metal content and not their form.