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	$245.87	12.852%	$277.4692	$277.47	$277.45	$277.50
Purchase #2	$118.53	8.638%	$128.7686	$128.77	$128.75	$128.80
Purchase #3	$50.75	12.192%	$56.9374	$56.94	$56.95	$56.90
Purchase #4	$157.53	11.570%	$175.7562	$175.76	$175.75	$175.80
Purchase #5	$208.86	6.530%	$222.4986	$222.50	$222.50	$222.50
Purchase #6	$157.87	6.274%	$167.7748	$167.77	$167.75	$167.80
Purchase #7	$107.47	4.789%	$112.6167	$112.62	$112.60	$112.60
7 purchase totals =	$1,046.88		$1,141.8215	$1,141.83	$1,141.75	$1,141.90