From the information supplied, noteably you worked for a bank I would assume these shares to be Exempt shares. That is the value of the shares at the time they were granted to you was less trhan $1,000. Under ATO rules they would have been held under a staff scheme until either you left the employment or a period of 3 years had elapsed, which ever occurred first.
Also at the end of the financail year in which you received those shares you/ your accountant should have completed a tax declaration in relation to those shares.
For CGT purposes the cost base of the shares is the unit price of the shares when you received them.
You should have received documentation from your employer outlining all of this. If this documentation has been lost then you will need to do the following.
You will need to find out if they have been converted from Employee shares to Ordinary held shares. The reason for this is if you try to sell them and they are still listed as Employee shares it could cost you money. Have a look on your last dividend statement or contact your previous employer. You may need to contact the employer in any event to determine the price of the shares when they were granted to you.
Once this price has been determined the CGT calcilation is simple:
Current Market value = Number of Shares by Current Share Price
Less
Cost Base = Number of Shares by Issue Price
Multiply the difference by 50%. This figure is then added to your assessable income and taxed at your marginal rates.
Good Luck.