Cash discounting is legal in all 50 states. The Durbin Amendment protects cash discount programs and sets federal guidelines for compliance. The federal guidelines require restaurants to disclose the details of the program to customers through signage and receipts, which is a best practice for informing customers about the benefits of the program. Cash discounting is different from credit card surcharges which are not legal in all 50 states. 

The advantages of a cash discount are for both restaurants and customers. Restaurants avoid paying expensive credit card processing fees, and customers save by spending less on each transaction. Cash discounts reduce costs, and savings are passed onto customers.