Jsonencode findet kommastellen wieder

$db->orderBy('sold_at','DESC');  
	$res = $db->get('transactions',1);  

	$rtn = array();
	foreach($res as $line)
	{
		$entry = array();
		$entry['pair'] = $line['pair'];  
		$entry['held'] = $line['sold_at'] - $line['buyed_at'];  
		$entry['buyprice'] = round($line['buyprice'],4);  
		$entry['sellprice'] = round($line['sellprice'],4);  
		$entry['profit'] = round((($line['sellprice'] / $line['buyprice']) -1) * 100,4) ;  
		$rtn = $entry;
	}
	echo '<pre>';  
	var_dump($rtn);
	echo '</pre>';  

	$str = json_encode($rtn);
	echo $str;

array(1) {
  =>
  array(5) {
    ["pair"]=>  
    string(7) "BNBUSDT"  
    ["held"]=>  
    int(2820)
    ["buyprice"]=>  
    float(15.2298)
    ["sellprice"]=>  
    float(15.497)
    ["profit"]=>  
    float(1.7545)
  }
}
[{"pair":"BNBUSDT","held":2820,"buyprice":15.2297999999999991160848367144353687763214111328125,"sellprice":15.4969999999999998863131622783839702606201171875,"profit":1.7544999999999999484856516573927365243434906005859375}]