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	$10.58	4.258%	$11.0305	$11.03	$11.05	$11.00
Purchase #2	$56.78	10.769%	$62.8946	$62.89	$62.90	$62.90
Purchase #3	$63.27	12.335%	$71.0744	$71.07	$71.05	$71.10
Purchase #4	$242.53	13.138%	$274.3936	$274.39	$274.40	$274.40
Purchase #5	$95.45	13.399%	$108.2393	$108.24	$108.25	$108.20
Purchase #6	$222.43	3.434%	$230.0682	$230.07	$230.05	$230.10
Purchase #7	$59.60	4.339%	$62.186	$62.19	$62.20	$62.20
7 purchase totals =	$750.64		$819.8866	$819.88	$819.90	$819.90