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	$15.75	9.678%	$17.2743	$17.27	$17.25	$17.30
Purchase #2	$175.32	13.438%	$198.8795	$198.88	$198.90	$198.90
Purchase #3	$101.57	9.786%	$111.5096	$111.51	$111.50	$111.50
Purchase #4	$206.41	3.855%	$214.3671	$214.37	$214.35	$214.40
Purchase #5	$160.47	7.297%	$172.1795	$172.18	$172.20	$172.20
Purchase #6	$155.27	3.732%	$161.0647	$161.06	$161.05	$161.10
Purchase #7	$51.45	8.695%	$55.9236	$55.92	$55.90	$55.90
7 purchase totals =	$866.24		$931.1983	$931.19	$931.15	$931.30