@babylove - The duties of a data entry clerk as you know, transfers data from paper into the computer.
The accounting clerks duties are to calculate numbers and input those figures into the system.
It may be that because so many companies are downsizing today is why you are seeing both job descriptions combined under one ad.
One or the other will be taking on both job duties as the accounting data entry clerk. This saves the company money and in return allows the data entry clerk experience with accounting procedures, and room for advancement.