Depends on the country/legal area.

In places like Europe and probably Asia, bitcoin is treated like currency so you can't just not pay tax on what you buy for not using fiat. For countries like America I'm not sure if sales tax can still be added on but I'd imagine it probably would be argued it could still be paid (especially if someone coverts those funds to cash at some point).

You pay transaction fees in btc. Whyd you want taxes on top of that? I'd just love to ltc or eth if that happens...