This is purely luck-based (supposedly). In the first machine, you need to have 3 of the Scatter figures (the totem heads that open their mouths) come up at the same time. You'll know you're close if the wheels start spinning crazily (although it can do this if there's a possibility of 5-in-a-row as well). Wilds don't count for this.
If you get the 3 heads, you'll go off to a different puzzle. There are three doors, each with a different amount of jewels. You have to find a key in each door before you find a skull.
The first door is guaranteed: there are three jewels, one key and no skulls. If you click on the two non-keys first, you'll get extra coins.
The second door is luck-based. Seven jewels, 2 keys and 1 skull.
The third door is also luck-based. 15 jewels, 3 keys and 2 skulls. If you make it past this door, you're into the treasure chamber, where you can choose 3 boxes with coins inside (top prize 2500 coins).
Do this five times and the achievement will pop.
(Fun fact: the odds of getting a key in the second door (assuming it actually IS a fair game) are 2/3, and the odds of getting a key in the third door are 3/5. The odds of making it through to the chamber from the beginning are 2/5, or 40%)
Good luck!