private void DisplaySales()
    {
        string selectQuery;
        selectQuery = "SELECT * FROM Sales";
        List<Sale> saleList = new List<Sale>();
        try
        {
            // Automatically  open and close the connection
            using (var conn = ConnectionManager.DatabaseConnection())
            using (var cmd = new SqlCommand(selectQuery, conn))
            using (var rdr = cmd.ExecuteReader())
            {

                while (rdr.Read())
                {
                    //Define the list items
                    var sale = new Sale(
                        int.Parse(rdr["SaleID"].ToString()),
                        int.Parse(rdr["CustomerID"].ToString()),
                        int.Parse(rdr["ProductID"].ToString()),
                        rdr["Payable"].ToString(),
                        DateTime.Parse(rdr["StartDAte"].ToString()));

                    saleList.Add(sale);
                }
                dgvSales.DataSource = saleList;
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show("Unsuccessful" + ex);
        }
    }