can't totally visualize this but here is an idea.
group on invoice number
create flag formulas for each invoice to determine the type (rent or property tax)
don't know your fields so this is a guess...
if table.lineitem='Rent' then 1 else 0
SUM this at the invoice number group level. This means if the SUM of that is >0 then this is a Rent invoice.
you can now use that as a formula condition in your running totals
Edited by DBlank - 08 Nov 2010 at 4:05am