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	$92.77	11.698%	$103.6222	$103.62	$103.60	$103.60
Purchase #2	$146.89	5.791%	$155.3964	$155.40	$155.40	$155.40
Purchase #3	$29.54	7.105%	$31.6388	$31.64	$31.65	$31.60
Purchase #4	$191.66	4.309%	$199.9186	$199.92	$199.90	$199.90
Purchase #5	$13.64	8.773%	$14.8366	$14.84	$14.85	$14.80
Purchase #6	$113.59	12.474%	$127.7592	$127.76	$127.75	$127.80
Purchase #7	$11.66	11.262%	$12.9731	$12.97	$12.95	$13.00
7 purchase totals =	$599.75		$646.1449	$646.15	$646.10	$646.10