Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$20.77	5.298%	$21.8704	$21.87	$21.85	$21.90
Purchase #2	$247.37	7.369%	$265.5987	$265.60	$265.60	$265.60
Purchase #3	$229.52	11.210%	$255.2492	$255.25	$255.25	$255.20
Purchase #4	$240.72	12.576%	$270.9929	$270.99	$271.00	$271.00
Purchase #5	$65.42	12.555%	$73.6335	$73.63	$73.65	$73.60
Purchase #6	$28.95	13.538%	$32.8693	$32.87	$32.85	$32.90
Purchase #7	$62.57	12.302%	$70.2674	$70.27	$70.25	$70.30
7 purchase totals =	$895.32		$990.4814	$990.48	$990.45	$990.50