adhawkins: You don't need to go back and change the prizes to a "fixed" amount just to deal with this issue. You can either (a) adjust the amount of one or more of the prizes (the "Adjust by" field takes a positive or negative amount); or (b) override the amount
That (changing them to a fixed amount) is what I've done.
I think it would probably be simpler to just keep taking an amount off the first prize (the amount of the rounding) until the prize total equals the prize fund.
Ok, this might not be exactly what everyone wants, but they'd still have the option of manually editing the prize fund once the rounding had been completed.
How does that sound?