If all your line items records containe a field that identifies the sale category, you can set up a list view layout based on your line items layout and use sub summary parts to compute the category sub totals. You probably already have a summary field that computes the total of your line item amounts. This is the field you can place in your sub summary part to get a sub total.
You set up your sub summary part with the category field as it's "break" or "when sorted by" field and then you must sort your line items records by this category field to see the sub totals.
On this layout, you can include the body layout part to list the individual line items sales, or you can remove this part if all you want to see is the total for each line item amount.
Here is a tutorial on summary reports that does produces both of these type reports: Creating Filemaker Pro summary reports--Tutorial
Thanks again Phil . will check it out