If you have the money and want to do it, I think you should give to each teacher. If it would hurt your budget or take something away from your family, then I'd only give to the homeroom teacher.
My oldest son is in highschool (no gifts anymore, except the Tide stain pen he gave to his German teacher lol ), so one down, but I have one in elementary. He gives his Main teacher (who is also his math teacher) and his reading teacher (they team teach and group by test scores) a nice gift. He's also giving his principal and the specials teachers an ornament (bought boxes of four, half off at Hobby Lobby) in a little basket ($1 each at Hobby Lobby) - just something to say we're thinking of them.
Crap - just realized we haven't planned on something for the bus driver and bus moniter. I'll have to buy some more!