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	$80.90	12.199%	$90.769	$90.77	$90.75	$90.80
Purchase #2	$55.91	11.257%	$62.2038	$62.20	$62.20	$62.20
Purchase #3	$149.83	5.189%	$157.6047	$157.60	$157.60	$157.60
Purchase #4	$197.61	4.178%	$205.8661	$205.87	$205.85	$205.90
Purchase #5	$53.45	11.266%	$59.4717	$59.47	$59.45	$59.50
Purchase #6	$155.90	12.793%	$175.8443	$175.84	$175.85	$175.80
Purchase #7	$211.92	9.440%	$231.9252	$231.93	$231.95	$231.90
7 purchase totals =	$905.52		$983.6848	$983.68	$983.65	$983.70