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	$18.56	13.830%	$21.1268	$21.13	$21.15	$21.10
Purchase #2	$143.39	8.255%	$155.2268	$155.23	$155.25	$155.20
Purchase #3	$52.57	13.258%	$59.5397	$59.54	$59.55	$59.50
Purchase #4	$62.46	13.485%	$70.8827	$70.88	$70.90	$70.90
Purchase #5	$209.25	11.763%	$233.8641	$233.86	$233.85	$233.90
Purchase #6	$195.86	4.289%	$204.2604	$204.26	$204.25	$204.30
Purchase #7	$205.56	8.787%	$223.6226	$223.62	$223.60	$223.60
7 purchase totals =	$887.65		$968.5231	$968.52	$968.55	$968.50