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	$79.32	13.747%	$90.2241	$90.22	$90.20	$90.20
Purchase #2	$120.63	9.114%	$131.6242	$131.62	$131.60	$131.60
Purchase #3	$115.73	3.814%	$120.1439	$120.14	$120.15	$120.10
Purchase #4	$145.27	9.288%	$158.7627	$158.76	$158.75	$158.80
Purchase #5	$134.49	6.643%	$143.4242	$143.42	$143.40	$143.40
Purchase #6	$171.66	8.176%	$185.6949	$185.69	$185.70	$185.70
Purchase #7	$158.37	11.559%	$176.676	$176.68	$176.70	$176.70
7 purchase totals =	$925.47		$1,006.5500	$1,006.53	$1,006.50	$1,006.50