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	$139.71	13.259%	$158.2341	$158.23	$158.25	$158.20
Purchase #2	$166.36	11.209%	$185.0073	$185.01	$185.00	$185.00
Purchase #3	$14.89	3.341%	$15.3875	$15.39	$15.40	$15.40
Purchase #4	$48.66	11.334%	$54.1751	$54.18	$54.20	$54.20
Purchase #5	$49.43	11.399%	$55.0645	$55.06	$55.05	$55.10
Purchase #6	$33.30	3.853%	$34.583	$34.58	$34.60	$34.60
Purchase #7	$60.50	4.350%	$63.1318	$63.13	$63.15	$63.10
7 purchase totals =	$512.85		$565.5833	$565.58	$565.65	$565.60