You can add a function to your report code that handles the divide by zero condition, this makes it a bit easier to implement in multiple cells, e.g.
Public Function Divider (ByVal Dividend As Double, ByVal Divisor As Double)
If IsNothing(Divisor) Or Divisor = 0
Return 0
Else
Return Dividend/Divisor
End If
End Function
You can then call this in a cell like so:
=Code.Divider(Fields!FieldA.Value, Fields!FieldB.Value)