Nikon D90 close-up attachment?

I want to buy a close-up attachment for my Nikon D90, to use with my 18-105mm VR lens, but I'm not sure which one to get. I spoke to a BH employee on their live chat, and he told me to get this one: http://www.bhphotovideo.com/...t_HMC.html
but, I don't understand why. What's the different between this one and a 77mm one? Which one's closer? I'm so confused. =P

The 67mm is the right one because it is the one that will fit the 18-105mm lens. Look on your lens. You will see a φ67 close to the serial number. That is trying to tell you the diameter of the threads on the front of your lens. 77mm wouldn't fit.