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	$111.27	5.707%	$117.6202	$117.62	$117.60	$117.60
Purchase #2	$36.74	6.552%	$39.1472	$39.15	$39.15	$39.10
Purchase #3	$91.75	9.463%	$100.4323	$100.43	$100.45	$100.40
Purchase #4	$105.41	12.758%	$118.8582	$118.86	$118.85	$118.90
Purchase #5	$128.95	9.399%	$141.07	$141.07	$141.05	$141.10
Purchase #6	$26.95	4.549%	$28.176	$28.18	$28.20	$28.20
Purchase #7	$176.94	12.761%	$199.5193	$199.52	$199.50	$199.50
7 purchase totals =	$678.01		$744.8232	$744.83	$744.80	$744.80