It's not a marketing trick. The sales tax situation in the USA is completely different than the VAT in the UK/EU. There are 50 states plus DC in the USA. Each state has their own sales tax and in many instances, some cities/towns have additional sales taxes imposed.
If sellers were required to post after tax prices, then they'd have to post tens of dozens of prices dependent on where their stores are located. Sure, that's not that big a deal at each individual store, but then you have to think about advertisements and printed material.
For the most part, American are used to it. We know what the tax rates are in our own states and surrounding locations. We can do the math to figure out the final price. It's not a big deal because we're used to it.