Join 2 Tables using datetime fields that are not exact matches

I need to join 2 tables using  datetime fields. Most of the corresponding entries in each table have the exact datetime down to the exact seconds. But some are up between  3 and 50 seconds different.
How can I add a tolerance so that the records join in the 2 tables.

Below is the SQL I'l using at the moment. On the first join I need a tolerance of 50 seconds and on the 2nd join I need a tolerance of 5 seconds.
SELECT     *
FROM         PhoneBill LEFT OUTER JOIN
                      PBXDATA ON PhoneBill.[Call Time] = PBXDATA.CALL_TIME AND PhoneBill.Duration = PBXDATA.DURATION