It is very rude, but having worked in retail for a fairly long time, and in several different companies, on balance, customers are far far ruder than staff.
I hate the word 'serve' as well. What am I, your scullery maid?
For what it's worth, I always tell them the amount, have a hand ready for the card should they give it to me, ask if they would rather have the receipt in the bag or in their hand. I rarely give change, but if I do, it would def be notes first. I'll also stop and hold the bag up by the handle while the customer puts away their purse. Even if they're chatting to friend/on the phone/ignoring me. I try to make conversation while the ridiculously slow card machine is going, even if it's just 'that top's a lovely colour, one of our girls wears it as uniform'. I work in an upmarket women's clothing shop and this is the basic that is expected.
However, I've also worked in Argos, and tbh, I don't think you can expect perfect service (argh) somewhere like that. Not downright rudeness, certainly, but if you're the 300th customer that person has served today, and 280 of them have been really rude, you do tend to lose your faith a little bit.