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	$138.96	12.637%	$156.5204	$156.52	$156.50	$156.50
Purchase #2	$233.57	8.611%	$253.6827	$253.68	$253.70	$253.70
Purchase #3	$110.56	5.467%	$116.6043	$116.60	$116.60	$116.60
Purchase #4	$35.41	12.545%	$39.8522	$39.85	$39.85	$39.90
Purchase #5	$182.45	9.738%	$200.217	$200.22	$200.20	$200.20
Purchase #6	$151.72	6.501%	$161.5833	$161.58	$161.60	$161.60
Purchase #7	$222.29	10.184%	$244.928	$244.93	$244.95	$244.90
7 purchase totals =	$1,074.96		$1,173.3879	$1,173.38	$1,173.40	$1,173.40