ASP.NET - Shopping cart calculation

I have a grid view and which contains the productname , price and the discount . Now i want that the Sales Tax and the Order discount is also shown according to its country and type of order . So how i implemented that.

How we implementes the Order discount menas we have to create a table in that or by any other type

Follow these links-

http://www.sitepoint.com/net-shopping-cart-datatables/
http://net.tutsplus.com/tutorials/other/build-a-shopping-cart-in-aspnet/

Try to place a dropdownlist populated with countries in one of the column

On the selectedindex changed you can populate your data

<asp:TemplateField>

 <ItemTemplate>

<asp:DropDownList ID="DropDownList1" runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">

</asp:DropDownList>

</ItemTemplate>

</asp:TemplateField>

You can populate the ddl like this

protected void grid1_RowDataBound(object sender, GridViewRowEventArgs e)

   {

     if (e.Row.RowType == DataControlRowType.DataRow)

     {

       string s2 = "select cname  from Country";

       SqlDataAdapter ada = new SqlDataAdapter(s2, con);

       DataSet ds = new DataSet();

       ada.Fill(ds);

       DropDownList ddl1 = (DropDownList)e.Row.FindControl("ddl1");

       ddl1.DataSource = ds;

       ddl1.DataTextField = "subDivisionName";

       ddl1.DataBind();

    }

   }

In the ddl changed event get the data

protected void ddl1_SelectedIndexChanged1(object sender,EventArgs e)

  {

     

  }

Regards