datagridview values under column[4] are not being summed as new rows are being added

private void saleslist_CellValueChanged(object sender, DataGridViewCellEventArgs e)
    {
        if (e.ColumnIndex == 4)
            total.Text = CellSum().ToString();
    }

    private double CellSum()
    {
        double sum = 0;
        for (int i = 0; i < saleslist.Rows.Count; ++i)
        {
            double d = 0;
            Double.TryParse(saleslist.Rows[i].Cells[4].Value.ToString(), out d);
            sum += d;
        }
        return sum;
    }