You have a place called Piggy Bank to save a portion of the coins you spend to spin in the game. Initially, your Piggy Bank has 5,000,000 coins, and with every coin spent, a portion gets saved there till it reaches its maximum limit, 100,000,000 coins. To get all these coins added to the account, you need to BREAK the Piggy Bank.
You can find the price for breaking the Piggy Bank inside the Piggy Bank button located at the Lobby screen's lower-right corner. After breaking one Piggy Bank, you'll receive another new Piggy Bank with 5,000,000 initial coins.
Figure: Screen capture of a piggybank