Provably Fair System for new Casino Game

I'm creating a casino game that multiple people can play. The basics of how it works are as follows:

1. A 10x10 grid of tiles is displayed to the players.
2. Players may purchase any number of tiles they like up to 10.
3. Once all tiles are purchased the game displays the winning tile.
4. Whoever purchased the winning tile wins the prize.

The winning tile is chosen at the start of each round and not shown until the end. How can I implement a provably fair system to show all the players the number chosen at the beginning was truly random and did not change?