Thanks to analysis of Trump's financial history conducted by the New York Times, we already know the GOP nominee hasn't paid taxes since 1995 because he declared a nearly billion dollar loss but never reported that the debt was cancelled, but it's possible he won't pay taxes ever again.
David Cay Johnston writing for The Daily Beast explains that claiming such a massive loss of $916 million will allow Trump to avoid paying taxes for the rest of his life.
Thanks to a Supreme Court opinion written by Justice Clarence Thomas in 2001, Trump was allowed to report a loss ($916 million) without actually suffering a loss (the debt was cancelled).
Justice Thomas apparently acknowledged that men like Trump could double their money by reporting losses without suffering any real losses, but he also wrote that it was "not the court’s concern."
Justice Thomas’s opinion was so egregiously at odds with economic reality that a few months later Congress—in a Republican-sponsored bill—shut down any further use of the scheme Trump employed. [...]
But while Congress stopped further abuse with passage of the Job Creation and Worker Assistance Act of 2002, it did not apply the new law retroactively nor did it limit losses to the date the bill was introduced.
Ordinarily, a person who posted a massive loss would be required to pay taxes again after their income exceeds the size of the loss, but in Trump's case that rule doesn't apply to him.
Because Trump manages his own real estate investments and properties, he could continue to avoid paying taxes under a loophole he lobbied for even if his income exceeds $916 million.
I recommend reading the full column at The Daily Beast to get a full grasp of how rich men like Trump can get away with obvious robbery.