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	$111.72	4.451%	$116.6927	$116.69	$116.70	$116.70
Purchase #2	$222.99	13.480%	$253.0491	$253.05	$253.05	$253.00
Purchase #3	$215.85	3.632%	$223.6897	$223.69	$223.70	$223.70
Purchase #4	$141.27	8.630%	$153.4616	$153.46	$153.45	$153.50
Purchase #5	$65.40	8.354%	$70.8635	$70.86	$70.85	$70.90
Purchase #6	$19.82	6.123%	$21.0336	$21.03	$21.05	$21.00
Purchase #7	$49.47	12.120%	$55.4658	$55.47	$55.45	$55.50
7 purchase totals =	$826.52		$894.2560	$894.25	$894.25	$894.30