[stronglikedan]

> For example, a bus line may prohibit payment of fares in pennies or dollar bills. In addition, movie theaters, convenience stores and gas stations may refuse to accept large denomination currency (usually notes above $20) as a matter of policy.

These are all examples where payment is being offered before service is rendered. OP is referring to instances where payment is being collected for services already rendered (i.e. debts).

[utrex]

OP is referring to some source of authority but not actually naming it. If OP is referring to the message on the Treasury notes, OP's interpretation is reasonable but OP should read more texts.

[stronglikedan]

OP qualified it with "Once services have been rendered", so OP's interpretation is exactly correct in that context.