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	$165.44	9.771%	$181.6051	$181.61	$181.60	$181.60
Purchase #2	$25.88	8.746%	$28.1435	$28.14	$28.15	$28.10
Purchase #3	$75.89	10.391%	$83.7757	$83.78	$83.80	$83.80
Purchase #4	$249.41	11.524%	$278.152	$278.15	$278.15	$278.20
Purchase #5	$106.97	11.733%	$119.5208	$119.52	$119.50	$119.50
Purchase #6	$95.61	5.210%	$100.5913	$100.59	$100.60	$100.60
Purchase #7	$119.73	6.762%	$127.8261	$127.83	$127.85	$127.80
7 purchase totals =	$838.93		$919.6145	$919.62	$919.65	$919.60