Paying a debt with coins.

Technically, a traffic ticket is not a debt; it’s a fine or punishment.

The U.K. Law was mentioned above – what others are you thinking of?

I did and it seems to refer to minor coins (1 and 5 cent coins, the ones that were not silver). I understood that the amount in pennies is limited to 25 cents, but the amount you can pay in dimes, quarters, half dollars, and dollar coins is unlimited. And yes a merchant can specify what he will accept for something, but debts are different. “All debts public and private” would seem to mean all debts public and private.

Hijack: I once dated a girl named Penny, so named because her parents had paid the obstetrician’s bill with a jar of 1500 pennies (this would have been the late '30s).

Here’s the Canadian one, in the Currency Act: