I try to be polite and would never walk in the building I work at and not say hello to the receptionist or security guards. that just seems rude to me.
As far as in places like the grocery store or post office type places it is hard not to say hello as most of us know each other here. I can't think of a way to not stop and say hi to the parents of my DD's best friend or my son's 5th grade teacher although I have to say I actually know my son's 5th grade teachers entire family from her parents to siblings too. It is that type of area.
My township actually got it's second grocery store a few years ago and it's first drug store maybe 4 years ago. I can't explain how excited people were to have that CVS open! It was like they had never seen a drug store before. When the new grocery store opened it had a line to the main hwy with people pushing their shopping carts like on black friday sales except this was a plain old Saturday and it was normally priced grocery store.
I have noticed now from my pt job that people go grocery shopping on the same day and time every week and go to the same cashier every time. So a lot of them actually look at it as an expected social interaction. While i like to consider myself friendly it is everything I can do to do everything I have to do to ring you u,p while answering a barage of questions. And it starts out with the ones I am required to say although i would ask how they are doing anyway.
But I will get things like how is DD doing at college?, What is her major again?, How is she liking living there? Is DS enjoying middle school?, Do you miss coaching soccer? And the list goes on and on and on!
And while I am trying to answer their questions and ask how their kids are doing, I am having an internal conversation of my own that is fighting to win with things like, cucumbers are 4162 and then the number of them, corn is 4077 and they probably have 10 because that is the sale, a bag of ice is 0875700007 and tell them they can grab it out of the case as they leave, the pineapple has a bar code but the round one won't scan so look in the drawer for the square one I put there last week. hey they have an Eagles jersey on and it is game day so I need to get the CSR to give me a 5% off coupon for their order, did that bakery item ring up right I thought it was BOGOF and on and on.
It really is more thinking that I have to do for my real job.
Who knew I was also being judged for being too friendly also.
I can relate although it is more of juggling. I may have several people on hold on the main phone line, visitors or patients stacked up at the desk with questions, plus electronic medical records to input and/or other tasks to do like Medicare letters, updating phone calllists, finding what used to be in our office which has been an adventure.
I will respond politely to someone that acts like either of them but I really don't need to talk to random people. I'm great at faking the friendly when I need to for work/social situations most of the time. 
