And for those who like shoving as much execution as possible into one line at the expense of readability:
Sub RoundedValue(x As Double) As Int
Return (x/Abs(x)) * 100 * Ceil(Abs(x)/100)
End Sub
If your y-axis could be any value within the Int range, you probably don't want to be rounding up to the next hundred. If value=1,854,025, you probably don't want your y-axis to go up to 1,854,100, you probably want it to go up to 2,000,000.
Sub RoundedValueGeneral(x As Double) As Int
Return (x/Abs(x)) * Power(10,Floor(Logarithm(Abs(x),10))) * Ceil(Abs(x)/Power(10,Floor(Logarithm(Abs(x),10))))
End Sub