No, the incentive would be for them to undercount as the money still ends up in the machine. $10 in the machine counted as $10 nets $1 in profit. $10 in the machine counted as $9 nets $1.90 in profit.
This would kill their business as TV news programs would show counting the money before it went into the machine and how much the machine claimed was counted. The fees that Coinstar rakes in are enough to ensure a great profit margin without actually stooping to miscounting coins.