Title 31 (Money and Finance), Subtitle IV (Money), Chapter 51 (Coins and Currency), Subchapter I (Monetary System), Section 5103 (Legal Tender) of the United States Code states:
<<United States coins and currency (including Federal reserve notes and circulating notes of Federal reserve banks and national banks) are legal tender for all debts, public charges, taxes, and dues. Foreign gold or silver coins are not legal tender for debts.>>
The Coinage Act of 1965 specified that all U.S. coins are legal tender in any amount. However, even in cases where legal tender has been agreed to as a form of payment, private businesses are still free to specify which forms of legal tender they will accept. If a shop doesn’t want to take any currency larger than $20 bills, or they don’t want to take pennies at all, or they want to be paid in nothing but dimes, they are entitled to do so.