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	$63.65	4.817%	$66.716	$66.72	$66.70	$66.70
Purchase #2	$250.89	7.674%	$270.1433	$270.14	$270.15	$270.10
Purchase #3	$187.80	12.280%	$210.8618	$210.86	$210.85	$210.90
Purchase #4	$38.32	6.315%	$40.7399	$40.74	$40.75	$40.70
Purchase #5	$117.57	13.635%	$133.6007	$133.60	$133.60	$133.60
Purchase #6	$154.89	11.495%	$172.6946	$172.69	$172.70	$172.70
Purchase #7	$13.31	13.325%	$15.0836	$15.08	$15.10	$15.10
7 purchase totals =	$826.43		$909.8399	$909.83	$909.85	$909.80