title: Round datetime object data with ±5 sec precision
body: <p>How can I round time with ±5 sec precision?</p>
  
  <pre><code>from datetime import datetime
  
  times = ['00:00:12.00', '00:00:12.5', '00:00:18.00', '00:00:58.00', '23:59:57.51']
  
  for time in times:
      obj = datetime.strptime(time, '%H:%M:%S.%f')
      rounded = obj  # todo round it with +-5 sec precision (how?)
      print datetime.strftime(rounded, '%H:%M:%S') + ',',
  
  # should print:
  # 00:00:10, 00:00:15, 00:00:20, 00:01:00, 00:00:00,
  </code></pre>