However, even if you lose money on the rounding of the commission, you still come out ahead versus a Place bet.
Since you have to pay 5% commission on Buy bets, you should bet in increments of $20 were the 5% is a whole number. I'm not an expert on Place or Buy bets, but my understanding is that you can bet anything you want. I know I have to bet at least the table minimum, but when my Place or Buy bets are above the minimum do I have to bet in increments of $5 on the 4 or 10?