I would not keep tiger barbs in a 5 gallon. They usually need to be in larger groups because the males can be very agressive when they go to mate and often times they will single out other males and harass them to death, and when they are in small groups they are also very nippy towards other fish.
With 5 gallons you are very limited as to what you can have. I would suggest if at all possible, you consider an Eclipse 12 system (12 gallons). It will give you a lot more options fish wise and it comes complete with everything you need for under 100 bills.