Should I go for 365cc, 385cc, or 415cc? Currently 5'5 105lbs. (photo)

How large you go depends on 2 things, your anatomy and your size desire.You appear to have a narrow breast so you may be limited with the size of implant that you can have placed. I think a 365 or 385 will be good for you. You will be a C cup for sure with those sizes. If you want to be larger than that then a 415 may work for you. In my practice I have patients try on the implants for a rough estimate. That usually helps with the decision making. You also need to trust your surgeon and make sure that the two of you are on the same page for sizing. I hope the has helped.

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins"). 
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.The key to obtaining a natural result is to stay within the parameters defined by your BWD. 
With regards to your specific question, I discourage patients from struggling over such a small volume differential. 45 cc is roughly equivalent to a shot glass and is unlikely to make a significant difference in outcome. If your goal is a natural outcome, conservative sizing is best (especially considering your smaller frame).
As always, discuss your concerns with a board certified plastic surgeon (ABPS).
Donovan Rosas MD
Board Certified by the American Board of Plastic Surgery
Member: American Society for Aesthetic Plastic Surgery, American Society of Plastic Surgeons
RealSelf Top 100
RealSelf Hall of Fame