In days past I would have idly wondered what these were and never worked up the energy to find out, but today all I have to do is Google on “Utah Sales Tax Token” and I instantly come up with this, which tells me that these are indeed tokens for paying sales tax. Starting in 1933 the sales tax rate in Utah was 2% and each token was worth one mill, or a tenth of a cent. Thus, a one mill token was the exact sales tax on a purchase of a nickel. Aluminum was in short supply during World War II, so they were replaced by plastic tokens, and then finally discarded in 1951.
Isn’t the internet remarkable?