Do I need the closing ?> tag

PHP 4.2.2 (linux) doesn't seem to mind if I leave off the closing ?> tag at
the end of a file.  Is the ?> assumed at EOF?

I have PHP that outputs binary and along the way I include() a lot of php
scripts.  I'm constantly having problems when I leave a little whitespace at
the end of some script after the ?> which screws up the output binary.
First time this happened it took me hours to figure out the cause.

What does everyone think about just leaving off the ?> as a solution to
this?  It works for me now, but would any PHP developer care to
prognosticate on the liklihood this might change in future?