Auto Compute Wheck Check In Repeater

I have a repeater that display a customer's bill. Now, the customer has the option to select which of the account he/she will pay. Therefore, in my interface, I have a checkbox in my repeater. All I wanted is to compute for the total amount to pay based on the selected checkboxes. Below is my code for my repeater under ItemTemplate.

Code:
<ItemTemplate>
<tr>
<td style="border: 1px solid #000;">
<asp:CheckBox ID="chkEntryCode" Text='<%# DataBinder.Eval(Container.DataItem, "Code") %>' runat="server" />
</td>
<td style="border: 1px solid #000;">
<asp:Label ID="lblRequestID" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "requestid") %>'></asp:Label>
</td>
<td style="border: 1px solid #000;"><%# DataBinder.Eval(Container.DataItem, "Description") %></td>
<td style="border: 1px solid #000;">
<asp:Label ID="lblAmount" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "Amount") %>'></asp:Label>
</td>
</tr>
</ItemTemplate>

And for me to compute for the amount to pay based on the checked checkboxes. I have the following code.

Code:

protected void rBill_ItemCommand(object source, RepeaterCommandEventArgs e)
{
double dAmountToPay = 0;
for (int i = 0; i <= rBill.Items.Count - 1; i++)
{
CheckBox chkItem = (CheckBox)rBill.Items[i].FindControl("chkEntryCode");
Label lblAmount = (Label)rBill.Items[i].FindControl("lblAmount");
if (chkItem.Checked)
dAmountToPay = dAmountToPay + double.Parse(lblAmount.Text);
}
lblTotalAmount.Text = dAmountToPay.ToString();
}

Well, based from the code I provided, there's nothing happens at all.