As you probably already have guessed this achievement is completely based on luck. It can take you five minutes, but also five hours.
With that in mind I have some little tips for getting this achievement.
First; make a save before you're trying to get this, so you can reload it when you either run out of money or when it's costing you too much and start all over.
Second; I got the achievement after throwing the selected dices a 2nd time. So you don't need to get five of a kind in a single throw. After your first throw you can select the dices which you want to throw again with
and hope you get lucky this time.
Third: Some of your opponents quit when you've thrown three of a kind with your first attempt. According to the comments there are some opponents who rarely quit after you've thrown three of a kind.
1. In the prologue; the soldier in the camp.
2. In act. 1; the monk in the basement of the inn in Flotsam.
Last: Winning games will be hard on the later stages of the game, as most opponents will quit, after you've thrown three of a kind. So go after this achievement as soon as possible.Edit
: apparantly when you throw 5 of a kind with your first throw and your opponent quits, you will not get the achievement.
This was posted in the comments by NeXuS23.
Also; the five and the six look a lot a like. So take a good look before you select which dice to roll again.
I did this early on in the first act in Flotsam after witnessing some events on the townsquare, and I had about 300 gold to try it with.
Took me over an hour and several reloads to get it eventually. Really hope you have more luck than I had.
There also is a youtube video which show you a way to increase your chance to get five of a kind, with a little trick.
Mind you that many people say this specific method didn't work for them and that it's totally luck based. I tried it myself and still had no luck after about twenty tries.
If I were you I would try it the first couple of times and when you don't get four of a kind within the first ten attempts, go back to the "normal" way of throwing the dices.