Roll Multipliers enable you to consume more Dice Rolls every time you hit the "GO!" button, increasing the rewards reaped accordingly! Activate Roll Multipliers by tapping the small button located just above and to the right of the “GO!” button! The more Dice Rolls you have in reserve, the higher your Multiplier can go!
 
On the top right of the GO! Button you will see a Roll Multiplier that you can change and adjust depending on the amount of rolls you have available. To do so tap on the button until you reach the max amount allowed (the color of the multiplier will change).

The multiplier will affect the rewards you obtain when you land on:

Rent tiles
Community Chest Tile
Corner Tile
Pick up’s
Tournaments and Event progress bar
Quick wins missions
Bank Heists and Megaheists
Shutdowns
Chance card rewards