How much money should I tip my limo driver?

Hello, my junior prom is coming up soon and it is located at leonard's in great neck, long island. me and my friends live in farmingdale and we are getting driven to leonards and then back to our houses. what is a reasonable tip to give the driver. if you dont live on long island, how much did you tip the driver and how many did each person pay. There are 9 people going in the limo.