Hm, I don't know of a rule that specifies how to use the word "about".
To me at least, "about 328 feet" seems okay. It gives you more precision than "about 300 feet" while still letting you know that it's not exactly 328 feet.
The point is that extra precision is unwarranted. We only know that it missed by somewhere between 50 and 149 meters, so it's not appropriate to imply that we know it more precisely.
This discussion reminds me of the time Apple quoted surprisingly precise weights for how much material they recovered through recycling[1]. It turned out the figures were converted from heavily rounded metric numbers.
The best part was that in the websites for some some markets they converted the very precise imperial figure back to metric and claimed something that was close to the original rounded number number but off enough to be extra weird (like 2,999 kg of silver).
