Yes, you can charge the tip to your room.
When you say 5 people, are they all in the same room? 3+2 could mean 3 adults and two kids, or 3 in one room and 2 in another.
If you're all in the same room, no problem.
If you're not all in the same room, you'll have to have two separate bills (unless you want to jump through some hoops in managing the ddp), but you can put all the tip on one check.