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	$244.90	12.194%	$274.7631	$274.76	$274.75	$274.80
Purchase #2	$10.30	3.733%	$10.6845	$10.68	$10.70	$10.70
Purchase #3	$46.90	4.352%	$48.9411	$48.94	$48.95	$48.90
Purchase #4	$144.46	8.599%	$156.8821	$156.88	$156.90	$156.90
Purchase #5	$118.73	7.579%	$127.7285	$127.73	$127.75	$127.70
Purchase #6	$34.99	10.194%	$38.5569	$38.56	$38.55	$38.60
Purchase #7	$66.32	9.325%	$72.5043	$72.50	$72.50	$72.50
7 purchase totals =	$666.60		$730.0605	$730.05	$730.10	$730.10