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	$243.27	9.619%	$266.6701	$266.67	$266.65	$266.70
Purchase #2	$53.49	11.340%	$59.5558	$59.56	$59.55	$59.60
Purchase #3	$55.74	9.766%	$61.1836	$61.18	$61.20	$61.20
Purchase #4	$144.92	9.310%	$158.4121	$158.41	$158.40	$158.40
Purchase #5	$50.38	11.315%	$56.0805	$56.08	$56.10	$56.10
Purchase #6	$72.99	8.307%	$79.0533	$79.05	$79.05	$79.10
Purchase #7	$125.51	12.757%	$141.5213	$141.52	$141.50	$141.50
7 purchase totals =	$746.30		$822.4767	$822.47	$822.45	$822.60