I can not comment due to my low reputation. I am not a lawyer, just want to contribute with my thoughts on this topic.
I agree with Patrick87 and phoog. As far as I'm concerned, and I've read, the default Legal Tender is paper (dollars) and coins in USA (each country has its Legal Tender). So, if a restaurant or business, do not want to allow pennies, or want to set a minimum amount of payment with debit/credit cards, they must have a visible warning/disclaimer or the waiter must acknowledge the customer beforehand. If they allow the customer to eat or get the service, and the customer can prove he/she was not informed, then the restaurant/business will have to accept the pennies. They can refuse to accept it, then you refuse to pay, then they sue you, then there is a very high probability you win the suit, because you had the money to pay and the restaurant refused to accept it, but it's a valid currency and you were not acknowledged before you eat the food. Unless, of course, like always happens, the restaurant printed the note in the menu in small print and they win.