The bank has to be able to cover a wager, so to roll $1 on any single number (say 13) requires the house to have what they advertise they pay out on that wager - usually 35:1 (plus your wager back) so the bank has to have $ 35 on hand to cover you wager.

A $20 wager = $700 on hand and so on.

I've seen where multiple players will use the "colour" chips of the game table and make a dozen different wagers each roll (usually with three or four chips) - they loose big, but win each roll as well.  Their lost chips cover the wins in the same roll.

Strange stuff to watch.