My wife's first name, so I think I need to say something.
Originally, Zheng means (1) "go on a journey" (foot + distant place). Later, which also naturally relates to kind of "military service".
I GUESS, the nature of this kind of forced "service" later make Zheng extend its meaning to a noun (2) tax;
Later as noun and verb frequently were used interchangeably, Zheng became a verb for taxing/collecting-tax, so Zheng has a third meaning (3) Collect/go-to-collect;
Then ZhengXun most probably appeared later, the word Zheng here is only related to an action of "go". You see it is still somehow related to the original meaning, however, its original meaning is weaker and weaker.
PS: Most of the Chinese characters lost their original meanings. Some however still keep them (Zheng is one of these). Still some may have multiple meanings from the very beginning.
Mostly, people don't care the original meaning, but for me, they are still helpful, especially, when you use it as your name.