I think you might have that backwars. First In are your older shares.

I have had to sell some of my Golden UNVC shares in the past for various reasons ( kid's weddings for one ). It killed to have to do so. I did profit each time in a major way BTW.
My oldest shares ( ,006 ) that were "Long" were the shares that were sold first, which consequently made my average go up, due to the fact I have purchased shares from .006 to .14.
You do bring up a big concern of many....taxation.
That has been brought up here on numerous occasion with some real good ( and some sketchy ) advice being offered up.

I myself will never sell short term shares.

I used the FIFO and my oldest shares ( Long ) were sold.
Someone with a better working knowledge of this than me please chime in.

Thanks 007