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	$15.99	8.698%	$17.3808	$17.38	$17.40	$17.40
Purchase #2	$104.81	6.359%	$111.4749	$111.47	$111.45	$111.50
Purchase #3	$23.89	11.377%	$26.608	$26.61	$26.60	$26.60
Purchase #4	$99.77	12.390%	$112.1315	$112.13	$112.15	$112.10
Purchase #5	$14.64	5.388%	$15.4288	$15.43	$15.45	$15.40
Purchase #6	$243.45	7.456%	$261.6016	$261.60	$261.60	$261.60
Purchase #7	$54.69	5.747%	$57.833	$57.83	$57.85	$57.80
7 purchase totals =	$557.24		$602.4586	$602.45	$602.50	$602.40