"Contrary to common misconception, there is no federal law stating that a private business, a person, or a government organization must accept currency or coins for payment. Private businesses are free to create their own policies on whether they accept cash, unless there is a specific state law which says otherwise. For example, a bus line may prohibit payment of fares in cents or dollar bills. In addition, movie theaters, convenience stores, and gas stations may refuse to accept large denomination currency as a matter of policy or safety.""The principal purpose of [the Coinage Act of 1965] is to ensure the nationwide acceptance of U.S. currency, consistent with constitutional language that reserves to Congress the power to create a uniform currency that holds the same value throughout the United States. While the statute provides that U.S. money is legal tender that may be accepted for the payment of debts, it does not require acceptance of cash payments, nor does it provide that restrictions cannot be imposed upon the acceptance of cash."
https://en.wikipedia.org/wiki/Legal_tender#United_States
