Is it standard practice to make sure that multiple, numbered citations occuring together are ordered?
In my experience, there is no particular necessity or requirement to ensure that numbered citations go in order.  Certainly, I have never personally encountered an instance with an IEEE or ACM publication (which use numerical order) where the publisher actually cared if this was the case.

That said, it certainly is much tidier to order the citations in a set, and doing so is very simple to do, so I often will do so if I notice they are out of order.

That said, there is one case in which I will not order the citations, and that is if a citation cluster has some citations that are more important than others.  In that case, I will always keep the citations ordered in decreasing importance instead, just to make it a little more likely for the reader to figure out which is the most important one.