tax question

Hi,

I have bought 3 parcels of the same stock at different prices over a 3 year period & want to sell some so I can offset the loss against some gains. The problem is I have made most of the loss on the shares I purchased more recently & therefore it would be more beneficial to sell these rather than the first batch I bought. The question is does the tax office have a ruling that says you must sell the first batch first or perhaps it does not matter?
PS. I paid 11 cents for the first parcel & 76 cents for the last so there is a big difference.

Thanks in advance

Mark