Because, unlike a thousandth of a dollar, those are valid amounts for real transactions.

It goes without saying that half pennies are dead. A mill seems to be from the Coinage Act of 1792, which is perhaps a tad outdated.

Take two half penny coins or notes to the bank and they’ll credit your account a penny. Of course, just like with the $500 or $1000 notes, you’ll be losing money on the deal.

> A mill ... is perhaps a tad outdated.

Yet you use mills every time you pay for gas. Pointless in that case? Probably. Still used all the time? Certainly.

I pull the gas lever intermittently until the gal goes up but the cents don't. It takes about 5 tries, but always makes me smile that I beat the game.