The IRS says any amount paid to get an item, including sales tax, shipping, etc or to make it ready for sale is part of item cost - so as far as the IRS is concerned it should be added to item cost and received at a price that includes all costs
States have what is often called a resellers permit, you download it, fill it out, give it to your vendor and then he can sell to you sales tax free for items you sell - that is the easiest way to deal with this in my opinion.
But if you want to track sales tax paid and claim a reduction in sales tax due when you file. When you receive inventory, on the expense tab, select a sales tax paid expense account (you will probably have to create it the first time).
This is the amount you will claim on the sales tax form, and this same amount has to be used to lower sales tax due in the pay sales tax module, using the adjust button.
This amount will not show on the sales tax liability reports though, you will just have to remember to use sales tax adjust.