From: http://en.wikipedia.org/wiki/Legal_tender#United_StatesThey can reject or accept any kind of payment they want. If they want to accept only credit cards with numbers ending in "3", that's OK. If they want to accept pennies, dimes, and Susan B. Anthony dollars (but not dollar bills), that's also legal. If they choose to accept beaver pelts, that's OK.
Legal tender or forced tender is an offered payment that, by law, cannot be refused in settlement of a debt, and have the debt remain in force. Currency is the most common form of legal tender.
In some jurisdictions legal tender can be refused as payment if no debt exists prior to the time of payment (where the obligation to pay may arise at the same time as the offer of payment). For example vending machines and transport staff do not have to accept the largest denomination of banknote. Shopkeepers can reject large banknotes — this is covered by the legal concept known as invitation to treat. However, restaurants that do not collect payment until after a meal is served would have to accept that legal tender for the debt incurred in purchasing the meal.