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	$59.60	11.862%	$66.6698	$66.67	$66.65	$66.70
Purchase #2	$108.76	6.662%	$116.0056	$116.01	$116.00	$116.00
Purchase #3	$229.70	10.707%	$254.294	$254.29	$254.30	$254.30
Purchase #4	$48.27	7.262%	$51.7754	$51.78	$51.80	$51.80
Purchase #5	$102.93	13.495%	$116.8204	$116.82	$116.80	$116.80
Purchase #6	$29.37	12.507%	$33.0433	$33.04	$33.05	$33.00
Purchase #7	$39.73	10.417%	$43.8687	$43.87	$43.85	$43.90
7 purchase totals =	$618.36		$682.4772	$682.48	$682.45	$682.50