Don't get sales tax confused with stamp taxes.
Stamp taxes are taxes you pay once you've 'acquired' the product, not sold it. Like cigarettes. When you buy a pack of smokes, there will be a stamp indicating a tax has already been paid on that item by the vendor( or somebody else in the distribution line ) The amount of taxes necessary vary by state.. but it looks like $3.50 per gram of weed vs. $200 per gram of other controlled substance ( cocaine, heroin.. etc )
This way, when a driver gets busted on the interstate with 100 kilos of cocaine and $1,000,000 in cash, the state steps in and grabs $200,000 in 'tax' revenue.. plus any penalties, I would imagine, right out of the $1,000,000 cash.