You can finesse your legend values by calculating new units in the attribute table, controlling significant digits and decimals in symbology's advanced labeling, AND normalize values right in the symbology pane! (Insert a new legend if you have converted your existing legend to a graphic)
TIMESTAMPS
00:00 Intro
00:15 Normalizing
01:00 Cleaning up new percent significant digits
01:22 Cleaning up class breaks
01:56 Updating the header to reflect new units
02:12 Inserting text to explain legend units of measure
02:45 Removing the layer name to avoid duplication
03:00 Converting to graphic to fine tune legend layout