I think all currency is legal to use, if I’m not mistaken. But it is the obligation of the business to make it work.
A business has the right to refuse the form of payment the customer wishes to use. A business could, if it wanted to do so, accept payments only in Russian rubles.
A smart business will be as flexible as they can be, but it was their right to not accept any particular form of payment they do not wish to accept.
Not quite.
Businesses and private citizens are free to determine what they will accept
for _payment_ of goods or services, e.g. “no checks accepted” “cash only”
“we accept credit cards”, whatever. The seller sets the terms.
A dollar denominated _debt_ is a different matter. They must accept payment in dollars, currently defined as US currency notes and coins.
Not sure about minor coinage though - they might be able to refuse pennies in amounts over $5.00, or at best the coins would need to be rolled. Most likely they will have to accept the pennies though.
What is interesting, if an offer to pay a _debt_ is refused, then the debt is no longer owed, for all intents and purposes. With all that said, it’s generally a bad idea to be a prick in this manner.