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	$110.25	11.613%	$123.0533	$123.05	$123.05	$123.10
Purchase #2	$222.39	7.291%	$238.6045	$238.60	$238.60	$238.60
Purchase #3	$235.79	3.254%	$243.4626	$243.46	$243.45	$243.50
Purchase #4	$131.84	9.286%	$144.0827	$144.08	$144.10	$144.10
Purchase #5	$247.65	10.137%	$272.7543	$272.75	$272.75	$272.80
Purchase #6	$241.53	4.131%	$251.5076	$251.51	$251.50	$251.50
Purchase #7	$6.78	8.479%	$7.3549	$7.35	$7.35	$7.40
7 purchase totals =	$1,196.23		$1,280.8199	$1,280.80	$1,280.80	$1,281.00