Firstly, it's psychological. If something is priced at �50 and something else is priced at �49.99 we are condition to want the lower price. It just sounds more attractive.
Secondly, its to stop shop emplyees keeping money. By pricing it at 99p, most people would pay with a �1 coin, therefore it forces the person on the till to open it in order to issue change.
Lol - well I guess a pound saving's better than none at all, and if you go shopping and buy 40 items at a penny less than the pound, you've saved yourself 40p - enough to buy a small packet of biscuits! : )
A lot of internet searches allow you to put your maximum spend limit as a search term - so if you put �70, it would bring results of �79.99 but not �80.
It's the first number that counts, so it doesn't stop at �69.99