If formulas already exist without the ROUNDUP function, you could add the
function using a macro.
Sub RoundUp_Add()
Dim myStr As String
Dim cel As Range
For Each cel In Selection
If cel.HasFormula = True Then
If Not cel.Formula Like "=ROUNDUP(*" Then
myStr = Right(cel.Formula, Len(cel.Formula) - 1)
cel.Value = "=ROUNDUP(" & myStr & ",3)" 'adjust the 3 to suit
End If
End If
Next
End Sub