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	$103.84	7.258%	$111.3767	$111.38	$111.40	$111.40
Purchase #2	$143.58	4.399%	$149.8961	$149.90	$149.90	$149.90
Purchase #3	$47.27	8.158%	$51.1263	$51.13	$51.15	$51.10
Purchase #4	$45.75	7.806%	$49.3212	$49.32	$49.30	$49.30
Purchase #5	$51.81	11.279%	$57.6536	$57.65	$57.65	$57.70
Purchase #6	$52.70	5.532%	$55.6154	$55.62	$55.60	$55.60
Purchase #7	$99.94	10.336%	$110.2698	$110.27	$110.25	$110.30
7 purchase totals =	$544.89		$585.2591	$585.27	$585.25	$585.30