If you bet five numbers, you should get 6.2:1 but are paid only 6:1. There are 36 numbers on a roulette wheel because it gives so many round number payouts. All of these take the minimum house edge. Usually, all bets pay off the fair amount if there were no zeros on the wheel, rounded down to the next lower integer.
While casinos differ somewhat, this is not quite true under the most common rules. All bets in roulette have the same return, except for one unusual one involving 0 and 00 which is a lot worse.
