When Vin's toenail was torn out, there was so much blood that it looked like someone had been murdered in that cage - there is a lot of blow flowing through the feet. It looks a whole lot worse than it is, though. I held him and scratched behind his ears while my mom held his foot in a cold, wet facecloth for five minutes or so and the bleeding stopped easily. If the bleeding hasn't stopped, do that. If it has, just keep an eye out for infection (if it's red and swollen after a few days, and/or if it smells funky) in which case get him to the vet so you can nip it in the bud. Some people will start abs anyways "just in case," but I don't recommend it as that's just building immunity to the medication and it won't be as effective when he really needs it.
If it seems like he's REALLY in pain, you can give him a very small amount of infant ibuprofen, though another forum member would have to give you the dosage info on that. For a toe injury, though, I doubt it's necessary. Odds are, you're a lot more upset and frazzled about this than he is.
Welcome to the world of rat ownership; I'm pretty sure these guys pay awake at night thinking of new ways to scare the snot out of us!
As a side note, Vin's toe grew back within a few weeks!