Being "nice" is not limited to the individual

[OakLeaf]

People carried cash.

And tax returns were filed by people with pencils who had to do all their calculations either by hand, or on a machine that was separate from the ledger that kept the books.

Sales tax was calculated on the spot by cashiers who had to hand-separate taxable from non-taxable items.

Recordkeeping, as much as the sales transactions, is impossible when computers are down (or would take way too much time for people to stand in line). And the IRS doesn't much care for approximations and guesses.