Watch it again.
The first two shots are obvious. Then you hear, but do not see him fire at the car as it starts to drive away/towards him, shot #3. Then you see him shoot, two times at the car, #'s 4 and 5. Finally, when the car is on its side, the last bad guy out of the bank gets round #6.
Then again, the bad guy jumping out of the car, once it is on it's side, gets off a shot too. That actually adds to the confusion.
I just dug out, and watched this movie (again) the day before this thread started, a classic.
I did the round count thing too.