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	$66.33	7.735%	$71.4606	$71.46	$71.45	$71.50
Purchase #2	$99.46	12.697%	$112.0884	$112.09	$112.10	$112.10
Purchase #3	$112.51	5.344%	$118.5225	$118.52	$118.50	$118.50
Purchase #4	$234.93	10.318%	$259.1701	$259.17	$259.15	$259.20
Purchase #5	$42.99	7.599%	$46.2568	$46.26	$46.25	$46.30
Purchase #6	$143.46	11.647%	$160.1688	$160.17	$160.15	$160.20
Purchase #7	$11.26	11.405%	$12.5442	$12.54	$12.55	$12.50
7 purchase totals =	$710.94		$780.2114	$780.21	$780.15	$780.30