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	$35.31	5.185%	$37.1408	$37.14	$37.15	$37.10
Purchase #2	$90.25	10.841%	$100.034	$100.03	$100.05	$100.00
Purchase #3	$169.57	5.744%	$179.3101	$179.31	$179.30	$179.30
Purchase #4	$95.87	9.167%	$104.6584	$104.66	$104.65	$104.70
Purchase #5	$44.96	10.851%	$49.8386	$49.84	$49.85	$49.80
Purchase #6	$21.36	11.229%	$23.7585	$23.76	$23.75	$23.80
Purchase #7	$20.71	3.472%	$21.4291	$21.43	$21.45	$21.40
7 purchase totals =	$478.03		$516.1695	$516.17	$516.20	$516.10