Hi.
i didn't traded so much of my crypto for FIAT so i didn't dealt with that question yet.
however i think it's an issue need to be dealt with.
1. do you use accounting services?
2.if so, do you keep documentation of all traded or bought coins?
3. what do you do in cases of profit from ICO's
WHAT SHOULD I DO??
Yes, I pay tax. Laws will vary depending on where you are in the world, but it is important to follow the rules and pay any taxes due. It is naive to think that crypto is anonymous and the authorities will never catch you.
In the UK, one thing that people may not realise is that crypto-to-crypto trades are taxable events, it's not just crypto-to-fiat. You do get a tax-free allowance under capital gains of around £11k per year, so if you are only dealing in small amounts then you are probably okay. It's always best to get professional advice though.