Specific Ads

I was in the store the other day and after I checked out I noticed some advertisements on the back of my receipt that seemed very specific or fitting for me and my purchases.  I had just bought some toothpaste and shampoo and on the back of my receipt was advertisements for dental floss and whitening aids for my teeth.  This just seemed very relevant to our conversation in class about how companies target specific ads to people and how they track almost everything that you do, such as what you buy or what you look at on the internet.