Rounding to the given nearest number of seconds in Ruby

round_nearest.rb

class Time
  def round_nearest(sec=1)
    down = self - (self.to_i % sec)
    up = down + sec

    difference_down = self - down
    difference_up = up - self

    if (difference_down < difference_up)
      return down
    else
      return up
    end
  end
end

# Results using Ruby v2.1.5p273

t = Time.now          # => 2016-03-31 00:42:30 +0300
t.round_nearest(60)   # => 2016-03-31 00:43:00 +0300
t.round_nearest(300)  # => 2016-03-31 00:45:00 +0300
t.round_nearest(600)  # => 2016-03-31 00:40:00 +0300
t.round_nearest(660)  # => 2016-03-31 00:43:00 +0300

t = Time.new(2015, 12, 29, 11, 46, 0)  # => 2015-12-29 11:46:00 +0200
t.round_nearest(60)   # => 2015-12-29 11:46:00 +0200
t.round_nearest(300)  # => 2015-12-29 11:45:00 +0200
t.round_nearest(600)  # => 2015-12-29 11:50:00 +0200
t.round_nearest(660)  # => 2015-12-29 11:44:00 +0200

t = Time.utc(2015, 12, 29, 11, 46, 0)  # => 2015-12-29 11:46:00 UTC
t.round_nearest(60)   # => 2015-12-29 11:46:00 UTC
t.round_nearest(300)  # => 2015-12-29 11:45:00 UTC
t.round_nearest(600)  # => 2015-12-29 11:50:00 UTC
t.round_nearest(660)  # => 2015-12-29 11:45:00 UTC