SELECT
    roundtime,
    Inbound_jam,
    Sorter_jam
FROM
(
    SELECT
        SUM(jam_area.Inbound_jam = 1) AS Inbound_jam,
        SUM(jam_area.Sorter_jam = 1) AS Sorter_jam,
        FROM_UNIXTIME(CEIL(UNIX_TIMESTAMP(jam_area.t_stamp) / 600) * 600) AS roundtime
    FROM jam_area
    WHERE jam_area.t_stamp BETWEEN :starttime AND :endtime
    GROUP BY FROM_UNIXTIME(CEIL(UNIX_TIMESTAMP(jam_area.t_stamp) / 600) * 600)
    ORDER BY roundtime ASC
) AS okeyjam;