Quote from jimrockford:
Suppose the best ask is 50.34, size 200 shares, and you offer 90 shares at 50.31. Your order will be visible on the books of island and arca, but will not be displayed in their top-of-book quotes, and will not be displayed in the NBBO.
Now suppose that somebody else comes and adds an offer to sell 30 shares at 50.32. A total of at least 100 shares will then become available, to anyone willing to pay 50.32 (they will get your 90 shares at 50.31, and they can have another 10 shares at 50.32, and maybe 20 more if they want it). If this happens, then an asking price of 50.32, rather than 50.34, will be disseminated for the market center, and it will be displayed in the NBBO.