Donald Trump has filed for bankruptcy four times and has used every legal loophole in the dirty book to keep his assets a secret ever since the 1980's. There is no doubt in my mind that there is still residual effects from many of them that still show in payments here and there and everywhere. The sheer amplitude and size of his returns means that errors could be possible and therefor scrutinized.
Donald Trump is likely hiding something from voters in his tax returns. Trump's refusal to release his returns is fueling speculation that there may be bombshells that would upset his supporters. Many have speculated that Trump overstates his income, as well as his charitable donations, especially to veterans groups. Donald Trump could clear up this speculation by simply releasing his tax returns.
Whether it is embarassing ties to a foreign government, like Russia's, or he's not as rich as he claims to be, Trump is hiding something. Perhaps it is that he hides his money in tax havens and pays virtually no tax. He's being audited for a reason, something isn't right about his finances.
Yes, Donald Trump needs to release his tax returns to prove he has nothing to hide. In the past, releasing tax returns to provide transparency has become a tradition for presidential candidates. Trump claims he is under audit and will not release his returns, but Mitt Romney released his returns when he was under audit. Due to his alleged connections with Putin, many of his opponents and supporters are now wondering whether he is financially supported by Russian interests. He may be hiding a Russian connection, but more likely his actual worth is far less than the ten billion dollars he claims. Releasing his tax returns would reveal how much money is really behind the billionaire candidate.