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	$40.81	5.714%	$43.1419	$43.14	$43.15	$43.10
Purchase #2	$50.71	9.306%	$55.4291	$55.43	$55.45	$55.40
Purchase #3	$120.66	13.389%	$136.8152	$136.82	$136.80	$136.80
Purchase #4	$93.69	6.185%	$99.4847	$99.48	$99.50	$99.50
Purchase #5	$94.42	6.420%	$100.4818	$100.48	$100.50	$100.50
Purchase #6	$245.58	3.733%	$254.7475	$254.75	$254.75	$254.70
Purchase #7	$124.57	12.732%	$140.4303	$140.43	$140.45	$140.40
7 purchase totals =	$770.44		$830.5305	$830.53	$830.60	$830.40