Headings ending in 5 is all very well, but what if you really wanted him on 270 deg. Could you say "turn left heading 275, then further left another 5"?
I propose using 271 or 276 to get around the Flight Levels +500ft problem mentioned by Throw a Dyce. Of course there will have to be situations where 269 or 274 will be used but these should be notified by the CAA and incorporated in MATS 2.