try this
<asp:GridView ID="GridView1" runat="server" ShowFooter="true" AutoGenerateColumns="false">
<Columns>
<asp:BoundField DataField="itemname" HeaderText="itemname" />
<asp:BoundField DataField="itemprice" HeaderText="itemprice" />
<asp:BoundField DataField="quantity" HeaderText="quantity" />
<asp:BoundField DataField="tax" HeaderText="tax" />
<asp:TemplateField HeaderText="finalamount">
<ItemTemplate>
<asp:Label Text='<%# Eval("finalamount") %>' runat="server" />
</ItemTemplate>
<FooterTemplate>
<asp:Button Text="Save" runat="server" />
</FooterTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>