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	$37.25	13.648%	$42.3339	$42.33	$42.35	$42.30
Purchase #2	$239.43	13.595%	$271.9805	$271.98	$272.00	$272.00
Purchase #3	$212.42	9.103%	$231.7566	$231.76	$231.75	$231.80
Purchase #4	$151.72	13.434%	$172.1021	$172.10	$172.10	$172.10
Purchase #5	$29.39	12.385%	$33.03	$33.03	$33.05	$33.00
Purchase #6	$128.29	5.135%	$134.8777	$134.88	$134.90	$134.90
Purchase #7	$47.91	9.173%	$52.3048	$52.30	$52.30	$52.30
7 purchase totals =	$846.41		$938.3856	$938.38	$938.45	$938.40