You can set the system to prompt for a deposit at a chosen percentage in the Misc. tab of Maintenance.

1. Tick the prompt for deposit amount checkbox
2. Type in what percentage of the order you would like to be paid as a deposit into the box

When you confirm an estimate dispense the following window will open and display the deposit amount:

Whichever amount you then select, either full amount or deposit, will automatically be ready to be paid on the till page. This amount can be changed once in the till if needed.