If he was put down on the roster to finish his shift at a certain time and he works a couple of minutes overtime without being asked he is most likely not to get paid the extra money. But if he was asked by the manager to work a bit longer he may have a chance to be paid that few extra dollars.
Answered - Customer Service (Former Employee) - Shepparton VIC
He is casual and probably doesn't receive overtime wages. The managers tell you to leave after your shift unless they need you in which case you'll be asked to work another hour or two paid.
Answered - TEAM MEMBER (Former Employee) - Rockhampton QLD
He should receive extra money as you are to paid for the amount of time you work. Also as he is 15, he should not be rostered to work past 10pm as per usual store contracts.
Answered - Cashier/Trainer (Former Employee) - Lalor VIC