echo json_encode($data, JSON_PRETTY_PRINT);

$data = ['some' => 'data'];
$json = preg_replace_callback ('/^ +/m', function ($m) {
  return str_repeat ("¥t", strlen ($m[0]) / 4);//空白数(4つ)で割った数分タブ文字を返却
}, json_encode ($data, JSON_PRETTY_PRINT));