This gave me retail flash-backs.
Exact change after the transaction people? I'd try to get their exact change back, but if I beat them to the punch I'd almost always have my drawer closed before they realised what I was doing, such as a $17.42 total, they have me a twenty, I've typed 20.00 into the PoS, then they hand me $0.42 expecting $3.00 in return... Unless you told me you had exact change, I probably had your change counted and in my hand before you even made the move to fumble for your exact change, and I'm holding $02.58 to give you with a closed drawer. (not) sorry sir? Not to mention that no matter how good you are with math, if you do cashier transactions all day like at a grocery store, if you stopped to work these out you will eventually make a mistake.
OP, on that one, I say just follow my advice and have their change counted and drawer closed, 99% of the people will not want to wait for your manager to come open your drawer. That 1% is hell, but worth it in my book.
People who pay with checks drive me insane. There's a reason so many places simply refuse to take them nowadays -- They're inefficient and annoy everyone involved. It's a decent amount of extra work for the cashier. I know it's a "quick" process, and easy, but it holds up the line. The line being slower means more frustrated people who have better things to do, and a delay from you doing work. It is also extra work on whoever deals with the stores finances - The checks have to go somewhere. More time for them to spend at the bank, instead of in the store... Working. (That last part is relatively moot, but still, screw checks).
Loyalty cards are just their own special little demon everywhere that has them, I feel. Great on the customer end but typically quite a pain in the rear on the employee side. I'm glad so many places make the customer stop and enter the number on a pin-pad these days, but that probably makes life a little more frustrating to everyone else. Learn your phone number, dude!
If they're on their phone when they get to me in line and don't put it down (A simple "Hey Mom, hold on!" is fine, and WILL make this quicker.) I either make it a point to be very boisterous in my questions, while not being belligerent, and make absolutely sure they answer questions. The second methdod is I completely ignore their existence just like they're ignoring mine. Oh, you had a coupon? You probably shouldn't have been on the phone (Asking if they have coupons is also almost never in a cashiers' spiel anyway), same for loyalty cards, accessories/upsells/addons/donations, and what have you.
I would always go very all-or-nothing with this particular annoyance I had. Most people knew better than to complain anyway, but even if they did, it's a very double edged sword to even try to punish an employee for doing either. "Oh, he's complaining that I offered him everything I'm supposed to offer each transaction?" (That's more of what I'd do -- Intentionally hit every point if they're on a phone. I'm not offering batteries to someone buying a candy bar, even though I'm supposed to). If they say you didn't offer anything, just say you didn't want to interrupt their call, or just say you did offer and got no response so you continued.
As for coupons, I can't figure out why most even have an expiration date anymore. It's ridiculous when so many stores have regional/district mandating that they accept expired coupons, meanwhile their competitor across the street (Where you work) does not. It's like restaurants slowly all joining together and comping less foor -- It sets the expectation that any complaint of a mild inconvenience = Free shit! Stop doing it, managers! Stand your ground, or people are just going to keep ignoring the coupon specifics and expect you to make it work regardless, and get more pissed off when you say no.