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	$131.31	11.292%	$146.1375	$146.14	$146.15	$146.10
Purchase #2	$66.98	5.741%	$70.8253	$70.83	$70.85	$70.80
Purchase #3	$127.43	8.377%	$138.1048	$138.10	$138.10	$138.10
Purchase #4	$42.96	12.866%	$48.4872	$48.49	$48.50	$48.50
Purchase #5	$12.40	7.640%	$13.3474	$13.35	$13.35	$13.30
Purchase #6	$36.54	5.577%	$38.5778	$38.58	$38.60	$38.60
Purchase #7	$142.50	6.156%	$151.2723	$151.27	$151.25	$151.30
7 purchase totals =	$560.12		$606.7523	$606.76	$606.80	$606.70