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	$33.88	12.384%	$38.0757	$38.08	$38.10	$38.10
Purchase #2	$87.69	13.261%	$99.3186	$99.32	$99.30	$99.30
Purchase #3	$138.43	7.523%	$148.8441	$148.84	$148.85	$148.80
Purchase #4	$34.28	12.393%	$38.5283	$38.53	$38.55	$38.50
Purchase #5	$105.72	4.456%	$110.4309	$110.43	$110.45	$110.40
Purchase #6	$246.84	13.269%	$279.5932	$279.59	$279.60	$279.60
Purchase #7	$215.30	11.733%	$240.5611	$240.56	$240.55	$240.60
7 purchase totals =	$862.14		$955.3519	$955.35	$955.40	$955.30