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.
What this statute means, in the words of the United States Treasury, is that "[A]ll United States money . . . is a valid and legal offer of payment for debts when tendered to a creditor. There is, however, no Federal law mandating that a person or organization must accept currency or coins as for payment for goods and/or services."
Maybe they don't have to accept 28,500 pennies...still worth a shot though, good luck getting that many pennies