Yes barcodes on screens can be scanned by traditional barcode readers. Just get the entire barcode to fit the screen, with all of it showing, and present it to the cashier. (im assuming you have digital coupons you can't or won't print)
Different stores do have different scanners... Not too long ago, Petsmart failed to scan a barcode off my 925 screen and that is higher pixel density than a 520 screen. Screen protectors may cause an issue as well. Now that I think about it I had a matte, anti-glare sheet on the 925.