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	$248.92	8.536%	$270.1678	$270.17	$270.15	$270.20
Purchase #2	$139.97	8.529%	$151.908	$151.91	$151.90	$151.90
Purchase #3	$34.27	3.560%	$35.49	$35.49	$35.50	$35.50
Purchase #4	$129.40	13.161%	$146.4303	$146.43	$146.45	$146.40
Purchase #5	$62.86	11.765%	$70.2555	$70.26	$70.25	$70.30
Purchase #6	$186.65	11.471%	$208.0606	$208.06	$208.05	$208.10
Purchase #7	$149.62	11.716%	$167.1495	$167.15	$167.15	$167.10
7 purchase totals =	$951.69		$1,049.4617	$1,049.47	$1,049.45	$1,049.50