According to the search results, proof coins are not specifically mentioned in the IRS rules regarding collectibles. However, the IRS does have rules regarding the treatment of collectibles in Individual Retirement Accounts (IRAs). Proof coins are not specifically approved or disapproved by the IRS. However, the IRS does have rules regarding the treatment of collectibles in IRAs, and proof coins may be subject to these rules if they are considered collectibles. It is recommended to consult with a financial advisor or tax professional to determine the specific tax implications of proof coins in an IRA.