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	$13.38	13.366%	$15.1684	$15.17	$15.15	$15.20
Purchase #2	$18.53	10.780%	$20.5275	$20.53	$20.55	$20.50
Purchase #3	$93.69	11.613%	$104.5702	$104.57	$104.55	$104.60
Purchase #4	$71.29	3.733%	$73.9513	$73.95	$73.95	$74.00
Purchase #5	$31.47	12.580%	$35.4289	$35.43	$35.45	$35.40
Purchase #6	$79.99	6.802%	$85.4309	$85.43	$85.45	$85.40
Purchase #7	$169.59	3.544%	$175.6003	$175.60	$175.60	$175.60
7 purchase totals =	$477.94		$510.6775	$510.68	$510.70	$510.70