Floating point values have a limited precision. Hence a value might 
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly 
printing it without any mathematical operations.

If you would like to know more about "floats" and what IEEE
754 is read this:
http://docs.sun.com/source/806-3568/ncg_goldberg.html
 
Thank you for your interest in PHP.

.

I can't belive that I will have to use my round functions in every new aplication I made? :-(

function roundit($val,$precision=0){
	$num=$val+(('0.'.str_repeat('0',$precision).'5')*1);
	$a=explode(".",$num);
	return  ($a[0].'.'.substr($a[1],0,$precision))*1;
}

function numberformat($number,$decimals='2',$dec_point='.',$thousands_sep=','){
	$number=roundit($number,$decimals);
	return number_format($number,$decimals,$dec_point,$thousands_sep);
}