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	$78.48	13.452%	$89.0371	$89.04	$89.05	$89.00
Purchase #2	$46.47	12.358%	$52.2128	$52.21	$52.20	$52.20
Purchase #3	$247.59	11.306%	$275.5825	$275.58	$275.60	$275.60
Purchase #4	$161.85	7.245%	$173.576	$173.58	$173.60	$173.60
Purchase #5	$130.79	7.526%	$140.6333	$140.63	$140.65	$140.60
Purchase #6	$66.73	12.296%	$74.9351	$74.94	$74.95	$74.90
Purchase #7	$122.41	4.489%	$127.905	$127.91	$127.90	$127.90
7 purchase totals =	$854.32		$933.8818	$933.89	$933.95	$933.80