This probably depends somewhat on jurisdiction as each state has its own rules on sales tax, but here in Illinois there is no sales tax on the purchase or sale of cryptocurrencies.  Their is, however, a capital gains tax that must be paid on the difference in the value of the cryptocurrency between when the it was acquired and when it was sold or used. Alternatively, the seller can take a capital loss deduction against other similar capital gains if the value at the time of sale or use is lower than at the time of acquisition.