As far as I know, there is a tax deductible per transaction. but it's not big enough. so it's quite unnoticed by most.
I think it just a fees and the listed exchanges will be the one to pay for the taxes. In my place its easy to convert bitcoin into fiat money without paying any taxes so I think it is still depend on the regulation on your country. If they required you to declare your income on bitcoin then follow that rules for you not to incur any problem, after all taxes are design for some good reason.