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	$40.43	5.521%	$42.6621	$42.66	$42.65	$42.70
Purchase #2	$29.48	11.443%	$32.8534	$32.85	$32.85	$32.90
Purchase #3	$108.30	7.720%	$116.6608	$116.66	$116.65	$116.70
Purchase #4	$69.30	4.300%	$72.2799	$72.28	$72.30	$72.30
Purchase #5	$99.75	5.703%	$105.4387	$105.44	$105.45	$105.40
Purchase #6	$44.71	7.730%	$48.1661	$48.17	$48.15	$48.20
Purchase #7	$184.40	3.268%	$190.4262	$190.43	$190.45	$190.40
7 purchase totals =	$576.37		$608.4872	$608.49	$608.50	$608.60