When we'd pay w/ cash, it was usually a "keep the change" type thing. Now, at all our local Sonics, they've installed card readers at each menu board & there's no place to enter a tip, as others have said. We don't go to Sonic all that often, & I guess I've just never given it that much thought.
But, speaking of tipping & automated systems...
Last night, DH was working & I wasn't feeling well, so I ordered dinner from a local Italian place through "Dinner Delivered." I always tip the pizza delivery person 20%, but I usually tip in cash & will round up to the nearest dollar which means he/she ends up w/ a little more than 20%. W/ the "Dinner Delivered" system, you HAVE to enter the tip when you place your order, & the site gives the user the option of 15%, 18%, or 20%. Again, I normally tip w/ cash, but, since I couldn't, I just clicked the 20% button which ended up being about 30 cents less than I would have tipped had I used cash. Definitely not a huge amount, but I do wonder why the site won't let a person NOT enter a tip portion &, instead, tip w/ cash at time of delivery because I know I'm probably not the only person who rounds tips up when tipping w/ cash.