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	$76.31	11.848%	$85.3512	$85.35	$85.35	$85.40
Purchase #2	$58.76	5.660%	$62.0858	$62.09	$62.10	$62.10
Purchase #3	$87.31	8.341%	$94.5925	$94.59	$94.60	$94.60
Purchase #4	$223.77	4.616%	$234.0992	$234.10	$234.10	$234.10
Purchase #5	$46.34	10.326%	$51.1251	$51.13	$51.15	$51.10
Purchase #6	$127.53	9.195%	$139.2564	$139.26	$139.25	$139.30
Purchase #7	$118.65	8.596%	$128.8492	$128.85	$128.85	$128.80
7 purchase totals =	$738.67		$795.3594	$795.37	$795.40	$795.40