I work part-time in retail and found that most people don't check their change as long as it is close to what they think they should get back.
I always tell the person the total for the sale, the amount of money they give me, the amount of the change, and then count the change for them. This works very well.
Most people are confused or impatient when I go that extra step start counting from the transaction total up to the amount of money they paid me, so I don't do it anymore.