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	$158.65	4.166%	$165.2594	$165.26	$165.25	$165.30
Purchase #2	$171.27	6.300%	$182.06	$182.06	$182.05	$182.10
Purchase #3	$67.35	11.581%	$75.1498	$75.15	$75.15	$75.10
Purchase #4	$133.47	12.233%	$149.7974	$149.80	$149.80	$149.80
Purchase #5	$123.54	4.367%	$128.935	$128.94	$128.95	$128.90
Purchase #6	$243.68	10.733%	$269.8342	$269.83	$269.85	$269.80
Purchase #7	$152.46	13.215%	$172.6076	$172.61	$172.60	$172.60
7 purchase totals =	$1,050.42		$1,143.6434	$1,143.65	$1,143.65	$1,143.60