[DocFarmer]

31 U.S.C. 5103

[Alberta's Child]

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.

So if I go buy a pizza at this place, am I: 1) paying off a debt, 2) paying a "public charge," 3) paying a tax, or 4) paying some kind of dues?

[Young Scholar]

"Legal tender" doesn't mean that only a given currency can be accepted, only that it must be accepted.

[KarinG1]

Sec. 5103. Legal tender

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.

So which are pesos, gold coins or silver ones? I have traveled a bit and have never found U.S. dollars unwelcome anywhere. In fact they are preferred in many places and can get you a discount on your purchase price.