Casino jackpots are building up wrong. Wheel of Money only adds 1 credit to the jackpot for all credit sizes but still takes the full amount (1, 3 or 5 credits) from your inventory. This means the Wheel of Money jackpot is building up a lot slower than it should be.
Grand Quest and Triple Diamonds both add 1,2,3 credits to the jackpot while taking 1,3,5 from the player.