Why bother? most Americans wouldn't understand the contents of his tax returns anyways, hell our tax code is so complicated even the scumbags in Congress that voted for its component parts don't understand it.
All releasing his tax returns would do is provide more fodder for the disingenuous talking heads in the media to distort, spin and outright lie about and they already have enough of that to keep them busy for the next 1000 years.
So, from now on, NO candidate for the WH should ever show their tax returns because.......well, because the average voter is too dumb to understand the intricacies of tax dodging, correct?