Parameters you have chosen to bill to the client will now be marked with a small green triangle in the bottom left hand corner of the cell. On the same note, items that you have chosen NOT to bill for, will have a red triangle in the bottom left hand corner.  

This will make it easy for you to differentiate between billed and non billed items. 

Here you can see the first dose of Cefazolin is billed for, while the second is not. 

Also, to include or exclude item from the billing, you can do some from the parameter calculator. If you have already added the item to the treatment sheet, you can change whether it is billed for or not it by tapping on the cell and toggling the billing option in the window.