The last part is made more complicated by having different tax rates on different items in different places at different times.
You see a national ad for Walmart with a widget on sale. Depending on what city and state you buy it, the price will change because the tax rates are different between and even within jurisdictions.
Maybe the Walmart you go to has a development agreement where they pay higher local tax as a way to cover the infrastructure project the City has to complete to support the building. Or maybe it’s the opposite and Walmart built a bunch of streets an utilities they dedicated to the City and now they don’t pay sales tax to the local jurisdiction.
Or maybe on September 1st sales tax rates changed in the middle of an ad campaign. Or maybe there’s an additional tax exemption due to a Development Agreement.
Or maybe that kayak is no longer taxed at the time sale because you bought a trolling motor at the same time and now it’s classified as a motor boat and the customer pays state sales tax when they register it with the state?
It’s really, really difficult to predict taxes when you’ve for so many wacky jurisdictional issues that affect the tax rate.