Hi. You should find a manual here:
http://www.devicemanuals.com/guide/Cash%20Registers/Sharp.html
To remove a percentage from the total sale, try this:
When you have entered all the items in the sale, press #ST
then type the percentage to remove eg 15
then press the % button
then press #ST again
Now you can continue as normal, and press a payment button to finish.
Hope this helps
Mark
Mark, June 2008