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??
No, i don't use accounting service
No, i don't document every trade or bought transactions as there are really too much
After selling to fiat, i always donate out 5-10% of my money to charity to help the world.
I believe when they got their aid or help, they become wiser and they will soon touch blockchain, this makes world a bigger and better place

It depends on your country's regulations. Mine doesn't have any regarding taxes for cryptocurrency income, profits, etc. (yet), so I have not had to deal with declaring that income, but if that time comes I will consult with an accountant.
Since I don't do many transactions I do have a record of my investments & bounty transactions. However, due to the anonymous / pseudonymous nature of most crypto wallets / accounts it might be hard to have them tax 100% of your transactions.
Like you, I have yet to exchange my crypto into fiat, but I did like @puremage111 donation idea.