Question for those with a driver (Beijing)

I'm fairly certain my driver is using me as an ATM machine. Once every month or two he presents me with an envelope full of receipts that totals Protected content , which I pay him. Thing is, he only drives me from my home to work four days a week, and neither place is pay to park, with an occasional trip on Saturday or Sunday. It just doesn't add up.

Is this fairly standard practice for drivers and I should just put up with it? Should I bother looking for a new driver (I'm happy with my guy otherwise)? Or is this possibly legitimate? The money isn't really the issue, I'm just not too thrilled with a person who I should be able to trust taking advantage of the situation.

Any advise or past experience is appreciated.

Thanks,
Steve