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	$62.71	5.514%	$66.1678	$66.17	$66.15	$66.20
Purchase #2	$56.76	10.728%	$62.8492	$62.85	$62.85	$62.80
Purchase #3	$141.86	11.843%	$158.6605	$158.66	$158.65	$158.70
Purchase #4	$63.98	11.153%	$71.1157	$71.12	$71.10	$71.10
Purchase #5	$68.41	8.729%	$74.3815	$74.38	$74.40	$74.40
Purchase #6	$148.81	13.806%	$169.3547	$169.35	$169.35	$169.40
Purchase #7	$138.44	9.738%	$151.9213	$151.92	$151.90	$151.90
7 purchase totals =	$680.97		$754.4507	$754.45	$754.40	$754.50