If you want a precise answer you'll need to provide more information about your data and data load script at a minimum, but if you're looking to do this in Qlik's engine script language it would likely be the following depending on your data:
TableWhatever:
LOAD *, If(Discount>= 0 and Discount<=.05,"Low",if(Discount>.05 and <= .1,"This level",if(Discount>.1 and Discount<=.15,"This Other Level",if(Discount>.15 and Discount <=.25,"Another level","No level"))));