That doesn't really tackle my point regarding that you don't know what your gains are, because you don't know which coins you are exactly selling. If they are all fractional-mined at different values, you are getting profits or losses depending on WHEN they were mined. There is no way to track that information.
It would be pretty easy to write a script, using the blockchain API to iterate all the mining receive transactions during the tax year on the receiving address(es) and to get a historical exchange values from the same API. The databases exist for free of charge, and you most likely have a computer that could run such a script.
please re-read my posts regarding the question remaining, how do you know which cashed out BTC, are from which exact mined BTC.
It helps zero to know, you received x btc at x price.
You need to know, that xyz bitcoin was recieved at xx price, and those same xyz bitcoin fraction was sold at yy price.