In the States, sales tax policies (and laws) vary from location to location.
For example, in CT, I had to charge sales tax on my *time* -- and, had to open a bank account solely for the storage of said taxes.
In many places, sales tax is termed "transaction privilege tax" or even "use tax". Often, the law states that failure of the seller to COLLECT that tax does not release the purchaser from the obligation to *pay* it!
E.g., when I purchase equipment "mail-order" (out of state) for my business, I have to track which sellers collected sales tax from me for that purchase (and, in theory, remitted it to the state) and which did not. For those that did not, I have to "out of the goodness of my heart" (:>) remit the equivalent funds in my monthly filing.
This can get complicated as different vendors may collect different subsets of the "total" sales tax *due*. Some will collect the same taxes that I would pay had I walked up to the corner store to make the purchase. Others may only collect the *state* portion of the sales tax. (we have state, county and city sales taxes, here)
Of course, you can pretend you didn't know this and FAIL to remit the taxes due. That, of course, is called fraud and opens up a whole can of legal worms... (an accountant/lawyer defending you would quickly consume more in fees than you could ever "save")