Surprised you don't have something like this[1], at the federal level:

" ...coins are legal tender for payment of amounts which are limited as follows:

    not exceeding 20c if 1c and/or 2c coins are offered (these coins have been withdrawn from circulation, but are still legal tender);
    not exceeding $5 if any combination of 5c, 10c, 20c and 50c coins are offered; and
    not exceeding 10 times the face value of the coin if $1 or $2 coins are offered.

"

It's clean, simple, and effective. And an entity can choose to accept the coins anyway if they wanted to, it just doesn't oblige them to accept them.

[1] https://banknotes.rba.gov.au/legal/legal-tender/