Fido

i was thinking of doing it through my bank institution. what if i increase the amount? Does fido return back my change? 

lets say your monthly bill is around 100$ and you set up a bill payment in your bank instution for 100$/month. if your next payment is around 104$, Would fido automatically take an extra 4$ or should I increase it to 105$? If i do the second one, wha...