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	$12.53	4.583%	$13.1042	$13.10	$13.10	$13.10
Purchase #2	$116.32	9.260%	$127.0912	$127.09	$127.10	$127.10
Purchase #3	$111.76	8.336%	$121.0763	$121.08	$121.10	$121.10
Purchase #4	$101.81	9.633%	$111.6174	$111.62	$111.60	$111.60
Purchase #5	$238.76	4.671%	$249.9125	$249.91	$249.90	$249.90
Purchase #6	$138.92	5.428%	$146.4606	$146.46	$146.45	$146.50
Purchase #7	$178.36	4.160%	$185.7798	$185.78	$185.80	$185.80
7 purchase totals =	$898.46		$955.0420	$955.04	$955.05	$955.10