PHP rounding, how many decimal places to keep, formatting numbers

/**1.number_format*/
$number = 1234.56789;
$nombre_format_francais = number_format($number, 2, ',', ' ');
$english_format_number = number_format($ number, 2, '.', '');


/**2.round*/
$number = 1234.56789;
echo round($number ,2);


/**3.sprintf*/
$formatted = sprintf ("￥%01.2f.", $money);
echo $formatted;

?>

Several digits, rounding, PHP