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	$118.29	8.392%	$128.2169	$128.22	$128.20	$128.20
Purchase #2	$136.58	13.745%	$155.3529	$155.35	$155.35	$155.40
Purchase #3	$175.32	11.494%	$195.4713	$195.47	$195.45	$195.50
Purchase #4	$56.94	4.676%	$59.6025	$59.60	$59.60	$59.60
Purchase #5	$165.87	7.696%	$178.6354	$178.64	$178.65	$178.60
Purchase #6	$40.80	13.580%	$46.3406	$46.34	$46.35	$46.30
Purchase #7	$33.94	9.831%	$37.2766	$37.28	$37.30	$37.30
7 purchase totals =	$727.74		$800.8962	$800.90	$800.90	$800.90