Hi Neetha,
If you did't want to use DataKeyNames instead of using Visible="false" in BoundField use ItemStyle-CssClass="hidden" HeaderStyle-CssClass="hidden" and apply display none in style css.
CSS
<style type="text/css">
hidden
{
display : none;
}
</style>
HTML
<asp:GridView ID="GridViewInvoice" runat="server" ShowHeaderWhenEmpty="true" DataKeyNames="DOID"
AutoGenerateColumns="False" CssClass="mGrid" HeaderStyle-CssClass="th" PagerStyle-CssClass="pgr"
Width="100%" BorderStyle="Solid" Style="overflow: auto" OnRowDataBound="GridViewInvoice_RowDataBound"
OnRowEditing="GridViewInvoice_RowEditing" OnRowDeleting="GridViewInvoice_RowDeleting">
<AlternatingRowStyle BackColor="#CCCCFF" />
<Columns>
<asp:BoundField DataField="Tax1" HeaderText="Tax1" SortExpression="Tax1" HeaderStyle-Width="7%"
ItemStyle-CssClass="hidden" HeaderStyle-CssClass="hidden" ItemStyle-HorizontalAlign="Right" />
</Columns>
</asp:GridView>