I would assume its the standard 3 to 6 years for auditing, but for something as crazy as hundreds of thousands of tickets, might be worth keeping around longer.
Yeah, that's basically what it is. The tickets that are still within the 6 year audit window have all been digitized; at this point I mostly keep them as a souvenir.
How did you digitize that many tickets?
High speed scanner, and an unreasonable amount of manual effort.
Why do you still keep them around? Edit: or for how long does the IRS make you keep them, I guess.