We’re not accountants or lawyers or the ATO, so we can’t advise on a specific case.
In general, this sort of reward is sporadic and not something people are going to do for a living, and will in most cases be only $10-$20 a week. It’s a bit like being a mystery shopper or filling out a survey and getting a small gift.
Whether you would pay tax on that would be a question for your tax person.
The exception is if you are a professional driver/courier. In that case, this is definitely income and we believe would probably be taxable.