If it is for each line/item then yes
1. Go to "Options"
2. Click on the tab "Other"
3. Untick the box beside "Do not show discount column on invoices/orders/qoutes"
Now you should be able to put in a % of discount into the discount column and the software will work it out for you ie
if an item price is 100 euros and you give a discount of 20% then the total will be 80 euros on the line