Sum of an Gridview Column should be shown in the last row of Gridview

Question

Dear Friends,
I have a Gridview name GridPODetails, in which there is a column named 
"Total", whatever the amount is in the total column its sum should be shown in that column but in the Last row or can say bottom of the column.
eg: Total
        200
        500
--------------
        700


how i can achieve this?

Regards,
Aamir