Back during a time when one US cent was actually worth something, various states issued sales tax tokens to account for fractions of a cent when computing tax. The tax tokens from Missouri are from the Depression era. They were used when the sale's tax on an item was less than a cent. Since Sales tax would be exact and there were no fractional cents to give change, the final price of an item was rounded up and the difference paid back to the customer in sales tax tokens. These tokens could be used to pay all or part of any sales tax at the time of another purchase.
The numismatic (coin collector) problem with these tokens is that they are made of zinc. Zinc corrodes like crazy, so most tokens you see today are ugly. If you can find a nice one, it is worth small amounts, as follows:
worn or corroded: a few US cents approximate catalog value
not corroded (like the token in our picture): $2 US dollars catalog value
There are also 5 mil Missouri tokens. They have a hole in the center and are worth the same as 1 mil tokens.