Shell petrol station i frequent

Ever since my dad bought another car and i've been driving it everyday, i always frequent this particular shell petrol station to top up Deasy's tank. I am a regular there such that i dont have to make payment first before refilling the tank (they require drivers to pay deposit first before they activate the pump so that people dont just leave without paying). I would just stand at where my pump is and raise my hand to ask them to activate my pump. They recognised me from afar and activate the pump without limit (means i have to make sure i dont over-pump the amount that i have at that moment. or else, i would not have enough money with me to pay them!).
Just recently, i paid them 10c short without realising it. Then i went to the kiosk to get something. I then left the kiosk, passing by the cashier and he did not stop or mention anything. Walked back to my car and i realised that i paid 10c less. So i went back to the cashier and gave the 10c. But its only 10c, if 10bucks better hor. I wonder would they stop me if i have given them 10bucks less. Maybe not coz they would have to replace the 10b shortage from their own pockets.
Such privilege i receive.