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	$70.94	4.543%	$74.1628	$74.16	$74.15	$74.20
Purchase #2	$66.32	9.710%	$72.7597	$72.76	$72.75	$72.80
Purchase #3	$133.87	12.845%	$151.0656	$151.07	$151.05	$151.10
Purchase #4	$108.27	10.698%	$119.8527	$119.85	$119.85	$119.90
Purchase #5	$86.64	3.724%	$89.8665	$89.87	$89.85	$89.90
Purchase #6	$17.46	10.672%	$19.3233	$19.32	$19.30	$19.30
Purchase #7	$49.46	9.284%	$54.0519	$54.05	$54.05	$54.10
7 purchase totals =	$532.96		$581.0825	$581.08	$581.00	$581.30