gistfile1.php

<?php

$sorted = array();
foreach($array AS $key => $value)
{
	$sort_key = (empty($sorted[$value['amount']]) ? $value['amount'] : $value['amount']+1);
	$sorted[$sort_key] = $value;
}

krsort($sorted);

<?php

$sorted = array();
foreach($array AS $key => $value)
{
    $sort_key = (empty($sorted[$value->amount]) ? $value->amount : $value->amount+1);
    $sorted[$sort_key] = $value;
}

krsort($sorted);