"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