Actually it's 1013.25"
There's not going to be answers that are that tight.
The range of answers will be targeted at using incorrect technique, eg. dry vs. wet lapse rates, 120'/hp instead of 30' etc....
AIP doesn't say round down, nor anything about intermediate QNHs.
It says observed values, ie. If their mickey doo baro says 1013.5, they will publish 1013.