getting sub-total after every five rows

Question

ItemName	Category	1st floor	2nd floor	total
Bedsheet
	wash	1	4	?
	fresh	3	5	?
	alter	8	6	?
	condemn	7	5	?
sub-total		?	?
pillow cover	wash	8	4	?
	fresh	2	3	?
	alter	8	8	?
	condemn	3	4	?
sub-total		?	?
so on

 This is a MSVS 2005 WINDOWS FORM APPLICATION. In this windows form application, I have datagridview and a show button, on clicking the show button data gets uploaded in the datagridview and this is the dynamic data from sql 2005 table which I am getting through a datatable I have created. Now my problem is how to calculate and get sub-total and Total figures in the above dynamic datagridview. please reply as soon as possible.