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	$151.93	12.171%	$170.4214	$170.42	$170.40	$170.40
Purchase #2	$70.82	7.409%	$76.0671	$76.07	$76.05	$76.10
Purchase #3	$215.36	4.495%	$225.0404	$225.04	$225.05	$225.00
Purchase #4	$245.92	13.644%	$279.4733	$279.47	$279.45	$279.50
Purchase #5	$89.92	10.739%	$99.5765	$99.58	$99.60	$99.60
Purchase #6	$238.72	5.168%	$251.057	$251.06	$251.05	$251.10
Purchase #7	$121.90	5.217%	$128.2595	$128.26	$128.25	$128.30
7 purchase totals =	$1,134.57		$1,229.8952	$1,229.90	$1,229.85	$1,230.00