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	$201.50	8.389%	$218.4038	$218.40	$218.40	$218.40
Purchase #2	$74.30	10.133%	$81.8288	$81.83	$81.85	$81.80
Purchase #3	$103.71	12.239%	$116.4031	$116.40	$116.40	$116.40
Purchase #4	$111.49	6.361%	$118.5819	$118.58	$118.60	$118.60
Purchase #5	$125.59	4.656%	$131.4375	$131.44	$131.45	$131.40
Purchase #6	$41.30	5.243%	$43.4654	$43.47	$43.45	$43.50
Purchase #7	$75.53	6.150%	$80.1751	$80.18	$80.20	$80.20
7 purchase totals =	$733.42		$790.2956	$790.30	$790.35	$790.30