Earlier quoted context omitted.
Surely he was also required to pay the extra costs for the transaction at the receiving end? I can't imagine the authority was somehow required to accept his coin payment, and not only accept but do it for free?
Yes, they were required to accept it. They are collecting taxes for the government (I'm not sure if the VA DMV is directly run by the government, or is a contractor doing business for the government, but it doesn't make a difference in this case), which means they have to accept legal US money, in any denomination, because of this section of US code, which he mentions on his website[0]: As per section 31 U.S.C. 5103…
Also: does the law imply that every public entity that you pay taxes to in the US must have a physical office somewhere that you can go pay with cash? Mind blown.