toFixed(n) truncates the number - it doesn't round it. <!DOCTYPE html>
<html>
<head>
<meta content="text/html;charset=utf-8" http-equiv="Content-Type">
<title>Number.toFixed()</title>
<script type="text/javascript">
var out;
function tf(n) {
out.innerHTML += n.toFixed(3) + '<br>';
}
function main() {
out = document.getElementById('out');
out.style.fontFamily = 'monospace';
tf(4 ); // 4.000
tf(4.2 ); // 4.200
tf(4.1004); // 4.100
tf(4.1009); // 4.100
}
</script>
</head>
<body onload='main()';>
<div id='out'></div>
</body>
</html>