php 如何自动省略小数点后的0

$str = rtrim(5.00100, 0);//$str=5.001

        $aa = '2021.0001';
        $a1 = explode('.',$aa);
        if($a1[1] > 0){
            $str = rtrim($aa, 0);
        }else{
            $str = $a1[0];
        }
        dump($str);
        dump($a1);
        die();