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	$16.72	12.849%	$18.8684	$18.87	$18.85	$18.90
Purchase #2	$219.62	13.635%	$249.5652	$249.57	$249.55	$249.60
Purchase #3	$7.32	4.495%	$7.649	$7.65	$7.65	$7.60
Purchase #4	$117.39	7.523%	$126.2212	$126.22	$126.20	$126.20
Purchase #5	$227.31	12.149%	$254.9259	$254.93	$254.95	$254.90
Purchase #6	$223.64	11.535%	$249.4369	$249.44	$249.45	$249.40
Purchase #7	$102.42	3.110%	$105.6053	$105.61	$105.60	$105.60
7 purchase totals =	$914.42		$1,012.2719	$1,012.29	$1,012.25	$1,012.20