JavaScript
<!DOCTYPE HTML>
<html lang="ja-JP">
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
</body>
<script type="text/javascript">
var data = 1254.56789;
var str = "";
str += Math.round(data) + "<br>";
str += Math.round(data * 100) / 100 + "<br>";
str += Math.round(data * 10000) / 10000 + "<br>";
str += Math.round(data / 100) * 100 + "<br>";
document.getElementsByTagName("body")[0].innerHTML = str;
</script>
</html>
PHP
<?php
header("Content-type: text/html; charset=utf-8");
$data = 1254.56789;
//小数点以下を四捨五入
echo round($data) . "<br>";
//小数第2位を四捨五入
echo round($data * 100) / 100 . "<br>";
//小数第4位を四捨五入
echo round($data * 10000) / 10000 . "<br>";
//百の位を四捨五入
echo round($data / 100) * 100 . "<br>";
?>