I'm not sure how the parent thinks it will help with shortages, but sales tax adds to the price that the consumer pays. On sales tax holidays you see prices go down.
It's the just-in-time nature of distribution. Demand doubles from "normal" and all of the sudden nothing is sitting on the shelf.
However, while no sales tax on hand sanitizers is hardly going to be of a measurable impact for an individual, when you're hoarding to squeeze people in crisis, no sales tax makes for a nice 'bulk discount'.