<ItemTemplate>
<asp:CheckBox Text="Taxable" runat="server" ID="Checkbox2" NAME="Checkbox1" />
 for(int i=0 ;i<MyDataGrid.Items.Count;i++)
        {
           CheckBox box = (CheckBox) sender;
         DataGridItem item = (DataGridItem) MyDataGrid.Items[i];
          if((item.ItemType  == ListItemType.AlternatingItem)||(item.ItemType == ListItemType.Item))
          {
            CheckBox boxx =(CheckBox) item.FindControl("Checkbox2");
            if(boxx.Checked  == true)
            {
              ///....
            }
         }