Assuming 5 minute interval:
irb(main):001:0> require ‘test.rb’
irb(main):002:0> n = strtotime(“7/28/2006 02:06:31.070”)
=> 1154070391
irb(main):003:0> remainder = n % 300
=> 91
irb(main):004:0> nr = date(n + ((remainder) ? (300-remainder):0))
=> “02:10:00”