Afrund dato til 10 minutters interval

select
  trunc(sysdate, 'mi')
  - numtodsinterval(mod(EXTRACT(minute FROM cast(sysdate as timestamp)), 10), 'minute')
from dual;

eller endda

select
  trunc(sysdate, 'mi')
  - mod(EXTRACT(minute FROM cast(sysdate as timestamp)), 10) / (24 * 60)
from dual;