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	$120.92	7.159%	$129.5767	$129.58	$129.60	$129.60
Purchase #2	$79.70	13.733%	$90.6452	$90.65	$90.65	$90.60
Purchase #3	$16.41	13.431%	$18.614	$18.61	$18.60	$18.60
Purchase #4	$40.85	4.858%	$42.8345	$42.83	$42.85	$42.80
Purchase #5	$235.66	6.522%	$251.0297	$251.03	$251.05	$251.00
Purchase #6	$5.25	3.261%	$5.4212	$5.42	$5.40	$5.40
Purchase #7	$28.71	12.611%	$32.3306	$32.33	$32.35	$32.30
7 purchase totals =	$527.50		$570.4519	$570.45	$570.50	$570.30