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	$108.94	7.142%	$116.7205	$116.72	$116.70	$116.70
Purchase #2	$44.76	4.873%	$46.9412	$46.94	$46.95	$46.90
Purchase #3	$94.90	8.853%	$103.3015	$103.30	$103.30	$103.30
Purchase #4	$76.56	6.278%	$81.3664	$81.37	$81.35	$81.40
Purchase #5	$71.58	12.522%	$80.5432	$80.54	$80.55	$80.50
Purchase #6	$45.27	5.780%	$47.8866	$47.89	$47.90	$47.90
Purchase #7	$29.91	12.341%	$33.6012	$33.60	$33.60	$33.60
7 purchase totals =	$471.92		$510.3606	$510.36	$510.35	$510.30