Hi David,
There is a way in the Report Designer to filter out certain item types. Before you open the Report Designer though, link the ItemType field from the Item table into the InvoiceLine table (you can do the same for the EstimateLine and PurchaseOrderLine tables, but I have used an invoice report in my example).
Now in the Report Designer, go to the properties of the DetailReport band. Click the button next to the Filter String property. Here you can add the filter, see my screenshot below:
This should filter out all ItemType's that equal 'SubTotal' from your report. Hope this helps!
Jason