You can apply discounts, service charges, taxes and any other detail you want to see on your bills.
Simply go to App Config and select "Configure Checkout Options". On the page that opens, you can insert discounts and charges to be used at checkout.
You can add as many options as you need from App Config and simply select the ones you want to apply to a ticket. Go to Orders and click on "Checkout" on the ticket you want to close. Then you can select the discounts and charges you want to apply to that specific ticket and the total amont will be calculated automatically.