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	$221.39	3.196%	$228.4656	$228.47	$228.45	$228.50
Purchase #2	$70.88	9.208%	$77.4066	$77.41	$77.40	$77.40
Purchase #3	$55.32	13.485%	$62.7799	$62.78	$62.80	$62.80
Purchase #4	$49.28	6.610%	$52.5374	$52.54	$52.55	$52.50
Purchase #5	$184.61	8.117%	$199.5948	$199.59	$199.60	$199.60
Purchase #6	$71.26	7.407%	$76.5382	$76.54	$76.55	$76.50
Purchase #7	$139.45	4.366%	$145.5384	$145.54	$145.55	$145.50
7 purchase totals =	$792.19		$842.8609	$842.87	$842.90	$842.80