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	$7.36	12.291%	$8.2646	$8.26	$8.25	$8.30
Purchase #2	$120.97	5.748%	$127.9234	$127.92	$127.90	$127.90
Purchase #3	$10.48	9.263%	$11.4508	$11.45	$11.45	$11.50
Purchase #4	$107.85	11.182%	$119.9098	$119.91	$119.90	$119.90
Purchase #5	$233.79	13.724%	$265.8753	$265.88	$265.90	$265.90
Purchase #6	$123.39	4.170%	$128.5354	$128.54	$128.55	$128.50
Purchase #7	$127.86	9.627%	$140.1691	$140.17	$140.15	$140.20
7 purchase totals =	$731.70		$802.1284	$802.13	$802.10	$802.20