I was asking this the other day. From my limited experience (around 15-20 thousand coins), I've noticed that what comes up in the slot machine on the first column is completely random, but for the other two columns, having a rhythm and being as precise as possible with it slightly increases your chances. I've burned through a couple thousand coins just randomly pressing stop as fast as I could, and I've hardly ever won that way. But whenever I've used the rhythym method, I've won a lot more times. Couple days ago I pulled up a metronome on Google and timed the stops with the ticks. Won 5/8 rounds (no jackpot, but 3 diagonals and 2 safes). Though it's probably a coincedence, and probably still mostly RNG.