quick answer is "no" - the nikon 105 is already a 1:1 (life-size) macro lens - at minimum focusing distance, you will be able to magnify the subject to the same size on your sensor (i.e. 1cm subject, 1cm on the sensor)
slightly longer answer is "it depends" - if you want to go for more more extreme magnification, you will need add-ons like raynox or tubes. this is useful for very small subjects, or if you want to fill up the whole frame with only a very small feature on the subject, like the eyes, or the head. but bear in mind that the larger the magnification, the shallower the DOF and the harder it is to get the subject into sharp focus - the slightest shake will lead to blur.
my suggestion is to stick with your macro lens first, and experiment with the flash to get the lighting effect that you want. magnification can come later.
