hi,
you need to write a common function in javascript that calculate the sum of all enter value in textbox that you want add.
for this first of all you need find out the textbox id and values.
for this see the aspx page in browser,see the id of textbox,
then write a common function in javascript and call it on onblur of textbox.
like that
<asp:TextBox CssClass="txtbox" ID="txtAmount" onblur="addvalue(this.id,this.value)" runat="server"
value='<%#Container.DataItem("amount") %>' MaxLength="15" Width="100px"></asp:TextBox>
function addvalue(id,value){
**write code here**
}
see control id like this
document.getElementById("grid1__ctl1_grid2__ctl1_txtbox1")