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	$7.46	11.854%	$8.3443	$8.34	$8.35	$8.30
Purchase #2	$169.92	12.148%	$190.5619	$190.56	$190.55	$190.60
Purchase #3	$42.49	9.679%	$46.6026	$46.60	$46.60	$46.60
Purchase #4	$235.53	8.733%	$256.0988	$256.10	$256.10	$256.10
Purchase #5	$14.76	3.137%	$15.223	$15.22	$15.20	$15.20
Purchase #6	$93.66	6.529%	$99.7751	$99.78	$99.80	$99.80
Purchase #7	$140.40	13.603%	$159.4986	$159.50	$159.50	$159.50
7 purchase totals =	$704.22		$776.1043	$776.10	$776.10	$776.10