I am not sure how it is done in the movies specifically but the reels are controlled by stepper motors.
A stepper motor uses a digital signal to tell it to go to position xx.
When you see your reels spinning there is a control program that is playing a control sequence of 1,2,3,4,5,6... and so on.
It could easily say 1, 18, 4, 19,7 and you would see your reels jump around pretty wildly.
So when the slot RNG picks 3 numbers - those are what the slot stops on.
You could easily connect up the reels to a small circuit and write a small program to say to move the reels to 1,6,2 and then 3,5,8 and finally 0,0,0 to simulate some one hitting the big one.
There is also movie magic --- show someone playing the slot, then do a cut scene to the reel test as Ken provided or even just manually move the reels into place and take a shot of the screen.......