You need to combine your totalCalc and subCalc functions into a single function.
You need subCalc to return TWO DIFFERENT VALUES, and it can't (easily) do that.
Separating them into two functions serves no purpose.
Also, kill your roundFloat() and checkAmount() functions. They aren't doing anything useful that can't be done simpler.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.