Yep a 1 mil tax coin. A more accurate way of paying taxes. I think to save the elderly money. It was worth 1/10 of a cent in 1935. 5 mils was worth 1/2 cent.
Although many people won't pick up a penny today, America was in the middle of the Depression in 1935 and a penny was important. But it was impossible to charge the correct tax on a sale if fractions of cents were involved. Rounding up meant the purchaser had to pay more and rounding down meant the merchant was cheated.
The mills made it possible for merchants to collect the proper amounts more accurately.