everything working just sub total and total not showing...

I have a bleep ts600 which I am using as a stand alone station for outside bars that I do throughout the summer. I have just put all of my products and prices onto it and when you press the item buttons they all come up in the top left hand screen displaying the quantity, item and price however all though this is displaying correctly the sub total, ammount paid and Total cost remains 0.00.

Please help brain is working overtime but with no joy yet...

Thanks in advance