This tool is still in development, but should currently help you collect the records you need for tax calculations. The historic currency rates are collected from https://cryptocompare.com, for most of 2017 this is interpolated hourly data, but from 2018 the colected data in minutely to improve accuracy in volatile market conditions.
The earliest date for which figures can be produced is 1st Jan 2017, and to improve the accuracy of figures, please cancel any open orders and don't carry out any transaction for one hour before using this. If your account was created after 1st Jan 2017 and you notice your starting 'Prior Balance' for STEEM or SBD is not zero, this indicates an error and you should not trust the figures. Please also let us know your account name in this case, so we can investigate. The starting 'Prior Balance' for VESTs will not be exact due to our approximation of the historic VESTS to STEEM ratio, but should be within acceptable limits.