When using your (Coles/Woolworth type) Fuel Discount Dockets to fill the car up, and you want to work out just how much fuel to put in so that you do not end up with a small amount of change when paying.
Simply enter in the amount of money you want to spend, the current full price of the fuel in cents per litre and set your docket saving amount.
This app from the information you enter will calculate what amount in dollars and litres to fill the car with so that at the cashier you pay in total the amount you wanted to spend. That way you wont end up with a small amount of change to fill your pockets.