If you want to go into process of calculating the GST%, it more than 7%. Take a cup of coffee for example. In 1994, Sugar up 3%, coffee powder 3%, milk 3%, and water 3%. End result coffee raised 10cents from 60c to 70c which is 16.6% increase.
And from GST 3% to 7%, we now see coffee at 90c from 70c which is 28.5%. It's not just 4% and 28% in total!
And if you look from 1994 to 2008, just 14 years we see 50% increase!