Why is sales tax instantly refunded after order completion?

I’ve been chatting with support and they haven’t given me an exact answer yet, just keep explaining how the system figures tax. Question; do you know if this sale is to a town/city that shares a zip with another town city and those two have different tax rates? For example, the customers physical address is town A, which shares a zip with town B but has a different tax rate, but they list town B as their address on the order? Shopify uses rooftop calculations, not zip based calculations, I think this may have something to do with this issue.