Line Chart - Allow padding of Y-axis range

The Y-axis options should include the ability to pad the auto-axis by a specific number or percentage.  That is, when using the Axis Range setting of Auto (or really, any of them) there should be an option to pad the range.  For example, if I'm looking at values between 0 and 100, I don't want the top value to be set to 100; I'd like to pad it to (max + 20%) resulting in a top axis value of 120.  If the numbers range from 20K - 30K, I'd like to pad both the min and max values by 5K.