A long time ago I had a bet with someone over something related to this, and the research involved (yes, lawyers were involved for legal opinions.. we take our bets to the rather ridiculous levels here...) covered this aspect.
If you roll into say a Best Buy and say "hey, I want to pay in pennies for this new TV!" they can refuse you service of course.
Essentially it boils down to the fact that there is NO law that says you must accept US currency as a form of payment.
However... There IS a law that states you must accept us currency for *debts*. This is where legal opinions differed, but in general it was decided that if for example you refused to pay your credit card bill with a check, and insisted on cash - and this matter got to court, the judge would force them to accept cash at that time to settle the case.
However, we did not get legal opinions re: the denomination of currency, or if coinage counted
I think it would come down to if you were purposefully fucking with someone over it or not. If some homeless guy needed to pay his $150 in coinage, I think that differs a lot from some asshole trying to screw with someone over sending 10 brinks trucks full of pennies.
Who knows though, it's a fun topic at least!
That said, this guy is a prick for wasting law enforcement's time over this. Absolute bullshit.
They are also wrong in that it's a "federal crime to not accept currency" - no such law exists, and I won a *very* substantial bet over this fact. You could perhaps make the argument an impound fine is a debt.. In which case the waters do get rather muddy.