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	$95.68	3.862%	$99.3752	$99.38	$99.40	$99.40
Purchase #2	$15.62	13.849%	$17.7832	$17.78	$17.80	$17.80
Purchase #3	$200.81	11.169%	$223.2385	$223.24	$223.25	$223.20
Purchase #4	$46.72	4.628%	$48.8822	$48.88	$48.90	$48.90
Purchase #5	$173.81	13.587%	$197.4256	$197.43	$197.45	$197.40
Purchase #6	$228.50	13.442%	$259.215	$259.22	$259.20	$259.20
Purchase #7	$216.26	8.162%	$233.9111	$233.91	$233.90	$233.90
7 purchase totals =	$977.40		$1,079.8308	$1,079.84	$1,079.90	$1,079.80