This misses the point though. The problem exists at any tax rate greater than zero. Doesn't matter if it's a penny or 100% of the price, the issue is that the advertised price is not the monetary value that's expected to be exchanged for that product/service.

However, this was intended to benefit border cities--Vancouver, WA in particular really liked it--but Washington State has no income tax and so is heavily reliant on sales tax. So, as of July 1 2019, the exemption (on state sales tax; local sales tax isn't covered here) may only be claimed post-transaction by the buyer: https://dor.wa.gov/taxes-rates/retail-sales-tax/sales-tax-ex...