Sometimes, when you click on a link through a search engine, a special promo code may automatically be entered and you will receive a discount. Such a discount will only be available if you entered the vendor's website through that specific link, so to answer your question, Yes, this is possible.
But like Shellguy said, when it comes to buying parts for building, I usually don't sweat a couple bucks here and there. What's more important is WHO you're buying from. Look for good customer service, good return policy, instock, etc.
Hope this helps.