Some do but not at the correct rate. At most, they are probably using the state tax rate only, not any special taxes that apply like city, county, regional. I'm curious about how anyone can estimate this - they would need to keep all receipts for all purchases and check to ensure that rate taxed (if any tax was applied) is the correct amount. I'm guessing the majority of people have to idea what the tax rate is for where they live or how to find it!
