If the ranges are the same and in your example that would be the case as each range is 5% then you can use the class function. What information are you dividing up? If the information is fixed it should just be a class(Field,5%,x,0). I'm not sure it is going to take the 5% as a number, but give it a try.
If the grouping is fixed you can also create these groups in the script. If the grouping is based on a calculation you may have to use an aggr() within the class function. For example, class(aggr(sum(Sales)/sum(total Sales),Customer),5%,x,0).
If the ranges are of varying lengths (e.g. 0-20%,20-100%) then investigate the valuelist function in the forum.
