*MAKE A SAVE BEFORE YOU BUY THE 5TH UPGRADE*
After you buy the 5th upgrade and turn in the order (Right on D-pad) it will trigger the end and you get to pick one person to go to the festival with. You get an achievement for picking each person. After you pick a person the game will end and the only option is a new game or load. Load your save at the end and pick a different person and get all the ending achievements :)
See in video at 4:20
Achievement Walkthrough: