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	$106.43	10.399%	$117.4977	$117.50	$117.50	$117.50
Purchase #2	$43.66	3.438%	$45.161	$45.16	$45.15	$45.20
Purchase #3	$17.83	13.782%	$20.2873	$20.29	$20.30	$20.30
Purchase #4	$101.59	9.748%	$111.493	$111.49	$111.50	$111.50
Purchase #5	$141.55	6.860%	$151.2603	$151.26	$151.25	$151.30
Purchase #6	$200.50	10.709%	$221.9715	$221.97	$221.95	$222.00
Purchase #7	$109.70	11.737%	$122.5755	$122.58	$122.60	$122.60
7 purchase totals =	$721.26		$790.2463	$790.25	$790.25	$790.40