It is doubtful that a municipality would have the authority to compel individuals to accept SomeVilleCoins for any debt.
The US government itself does not have the power to compel individuals to accept federal currency as payment. 31 USC 5103 says that "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", which means that they are "a legal offer of payment for debts when tendered to a creditor". But no Federal statute mandates that a private business, a person or an organization must accept currency or coins. "Legal tender" does not mean "the only legally usable form of money", it means "it is legal to tender an offer in terms of it".
State paper currency would not be allowed given Art. 1 §10 Cl. 1 of the US Constitution, which says that
No State shall enter into any Treaty, Alliance, or Confederation;
grant Letters of Marque and Reprisal; coin Money; emit Bills of
Credit; make any Thing but gold and silver Coin a Tender in Payment of
Debts; pass any Bill of Attainder, ex post facto Law, or Law impairing
the Obligation of Contracts, or grant any Title of Nobility
The HOUR currencies are "optional", and nobody is compelled to accept them as opposed to federal dollars.