When you have a field that is formatted as a percentage, for that field to display correctly, the user should enter the number as a decimal, i.e., for 10%, they would enter .1, for 17.5%, they would enter .175. However many people are used to entering a whole number and expect it to display as a percentage.
The script below should be attached to every percentage field in your solution as a script trigger OnObjectExit. It checks to see if the value has been entered as a whole number, i.e., >= 1 and, if so, divides it by 100. Otherwise it leaves it alone.