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	$47.30	13.233%	$53.5592	$53.56	$53.55	$53.60
Purchase #2	$139.72	8.412%	$151.4732	$151.47	$151.45	$151.50
Purchase #3	$214.31	3.223%	$221.2172	$221.22	$221.20	$221.20
Purchase #4	$70.71	12.450%	$79.5134	$79.51	$79.50	$79.50
Purchase #5	$78.58	11.306%	$87.4643	$87.46	$87.45	$87.50
Purchase #6	$102.83	8.741%	$111.8184	$111.82	$111.80	$111.80
Purchase #7	$100.93	12.237%	$113.2808	$113.28	$113.30	$113.30
7 purchase totals =	$754.38		$818.3265	$818.32	$818.25	$818.40