Tax on any obtained profit resulted from   crypto related activity ^{sell, exchange, pay for goods} has to be paid in accordance with the regulation of the given country. Some countries exempts  matured  crypto  i.e. crypto which is in users wallet for the long period of time while others don't allow any exemption. The attempt to hide your crypto-profit from taxation may result in the penalty, jailing including, similar to early BTC investor who was " jailed for unreported crypto gains in $4M BTC sale".