I've paid for two routines: $350 arranged at our own gym and $500 arranged privately. In both cases the fees were clearly set forth ahead of time, and we did not feel a need to tip on top of that. There was nothing awkward about paying in either circumstance, plus I'm pretty sure our own gym would have told us if a tip was proper etiquette.
The only tipping done that I've heard of was for a young choreographer who charged merely $100. I think some parents tipped her because she did better routines than the previous $350 ones, so they felt like she undercharged and wanted to compensate her properly.