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	$99.35	12.152%	$111.423	$111.42	$111.40	$111.40
Purchase #2	$162.61	6.714%	$173.5276	$173.53	$173.55	$173.50
Purchase #3	$68.39	10.326%	$75.452	$75.45	$75.45	$75.50
Purchase #4	$143.93	12.692%	$162.1976	$162.20	$162.20	$162.20
Purchase #5	$243.28	9.609%	$266.6568	$266.66	$266.65	$266.70
Purchase #6	$62.60	13.847%	$71.2682	$71.27	$71.25	$71.30
Purchase #7	$121.75	5.864%	$128.8894	$128.89	$128.90	$128.90
7 purchase totals =	$901.91		$989.4146	$989.42	$989.40	$989.50