Long time ago, in many niches smart marketers used 9 instead of 0, because psychologically when people see $19 instead of $20, they think that $19 is much lower and this little trick increased the sales greatly.

But after a while, people subconsciously rejects the 9 trick, so marketers had to come up with something new... And they did! They changed the angle of attack and took 7 instead of 9. 7 is also referred as "lucky" number, and people like it.

But nowadays, in my opinion, product prices are ending in 7 just because everyone else does it, everyone just follows up the trend without even thinking