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	$45.73	5.448%	$48.2214	$48.22	$48.20	$48.20
Purchase #2	$40.52	6.337%	$43.0878	$43.09	$43.10	$43.10
Purchase #3	$44.54	9.115%	$48.5998	$48.60	$48.60	$48.60
Purchase #4	$59.40	6.730%	$63.3976	$63.40	$63.40	$63.40
Purchase #5	$17.84	5.487%	$18.8189	$18.82	$18.80	$18.80
Purchase #6	$139.54	11.159%	$155.1113	$155.11	$155.10	$155.10
Purchase #7	$156.40	10.193%	$172.3419	$172.34	$172.35	$172.30
7 purchase totals =	$503.97		$549.5787	$549.58	$549.55	$549.50