As has probably already been stated, that's 4.2 billion pennies - i.e. an integer overflow. I agree that slot machines shouldn't have these issues, but by the same token, if a machine whose posted top prize is, say, $10,000 says that I won $42 million, I would expect that there's an error. Similarly, if my bank has a computer error and tells me that I have an extra $1 million in my account, I wouldn't expect them to honor the error.

Oatmeal? Spittle? Semen? This must be where Wilford Brimley was strangled by Bob Crane!