Yes! I did it! You have to keep hitting cards untill you have 5 in total and then BANG! It is very easy it just depends on luck only..
Silly me.. I was thinking this trophy might be taking a long time to get..
My beautiful simple strategy for this trophy is:
1 ~ Buy medals. (I chose the maximum number)
2 ~ Go to blackjack.
3 ~ Select play.
4 ~ Choose 10 medals.
5 ~ Keep choosing hit untill you luckily have 5 cards in total.
Just continue doing this strategy till you hear the trophy's sound it is as simple as that..!