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This is usually mostly circumvented by demanding "EXACT CHANGE" though. In most states, there are sales tax at several levels that don't apply uniformly, so it is nearly impossible or too time-consuming to use cash, because you simply don't know how much you'll have to pay.

Why does the company not give you an invoice for the exact amount?

You are correct. https://malegislature.gov/Laws/GeneralLaws/PartIII/TitleIV/C...

It’s a Federal law and written on every bill, “this note is legal tender for all debts, public and private.”

That pertains to debts - it’s legal to have credit/debit only stores; you see them at times.

concerts do this more and more now, festival wristbands with preloaded cash etc