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	$42.70	7.291%	$45.8133	$45.81	$45.80	$45.80
Purchase #2	$33.67	5.147%	$35.403	$35.40	$35.40	$35.40
Purchase #3	$52.79	8.834%	$57.4535	$57.45	$57.45	$57.50
Purchase #4	$242.95	6.633%	$259.0649	$259.06	$259.05	$259.10
Purchase #5	$70.47	3.125%	$72.6722	$72.67	$72.65	$72.70
Purchase #6	$58.96	4.322%	$61.5083	$61.51	$61.50	$61.50
Purchase #7	$15.50	5.721%	$16.3868	$16.39	$16.40	$16.40
7 purchase totals =	$517.04		$548.3020	$548.29	$548.25	$548.40