sort.php

<?php
$data = json_decode($json, true);

uasort($data['allresults'], function($a, $b) {
	$aSalary = $a['results'][0]['salary'];
	$bSalary = $b['results'][0]['salary'];

	return $bSalary < $aSalary;
});

foreach($data['allresults'] as $item) {
	printf("%s: %d<br />", $item['results'][0]['Name'], $item['results'][0]['salary']);
}