code: def round_60(value):
      
      t = 60
      if value is not None:
          r = value % t
          if r > t / 2:
              ret = value + (t - r)
          else:
              ret = value - r
      else:
          ret = NaN
      return ret
docs: round the number to the multiple of 60
  
      Say a random value is represented by: 60 * n + r
      n is an integer and r is an integer between 0 and 60.
      if r < 30, the result is 60 * n.
      otherwise, the result is 60 * (n + 1)
  
      The use of this function is that the counter refreshment on
      VNX is always 1 minute.  So the delta time between samples of
      counters must be the multiple of 60.
      :param value: the value to be rounded.
      :return: result