Could you elaborate on why this would not be the expected behavior?

Also zero and negative zero are defined to compare equal, so I'm not sure whether this makes any difference in practice.

Computers use a standard described in IEEE-754 to handle floating point values. 
IEEE-754 uses -0 to describe values that approach 0 from a negative value. You 
will see the same thing in any language that uses the computer's built-in 
floating point mechanism. C, Python, Ruby, Perl, etc. For example in Python:

>>> round(-0.1)
-0.0

You can read more about it at:

http://en.wikipedia.org/wiki/Signed_zero

If the -0 is expected, then this indeed was wrong in some PHP versions:

<?php
$value = -2.2204460492503E-16;
$round = round($value, 4);
var_dump($round);

Output for 4.3.0 - 5.2.0, 5.3.4 - 5.3.6, hhvm-3.0.1 - 3.3.1
float(0)
Output for 5.2.1 - 5.3.3, 5.3.7 - 5.6.3, php7@20140507 - 20141101
float(-0)

see http://3v4l.org/OcEso

0 and -0 are equivalent, so if this is causing any sort of issue in your code you need to fix your code. You can read all about rounding in PHP here:

  https://wiki.php.net/rfc/rounding