The grocery store price check fiasco that saved me $47

Last Tuesday I was in line at a Kroger outside Nashville and watched the person in front of me get charged $9.99 for a bag of coffee that was on a shelf tag for $6.49. They didn't notice, so I pointed it out to the cashier. She fixed it and I started checking my own receipt, turns out my salsa rang up wrong too. I saved $4 on mine, but the cashier told me that most people never catch these errors. Now I spend three minutes at the register scanning my receipt before I leave the parking lot. How often do you actually check your grocery receipts for price mistakes? My guess is almost never, and that's money you're just handing over.