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	$115.52	13.825%	$131.4906	$131.49	$131.50	$131.50
Purchase #2	$61.63	8.497%	$66.8667	$66.87	$66.85	$66.90
Purchase #3	$190.99	11.612%	$213.1678	$213.17	$213.15	$213.20
Purchase #4	$54.87	12.108%	$61.5137	$61.51	$61.50	$61.50
Purchase #5	$128.28	3.355%	$132.5838	$132.58	$132.60	$132.60
Purchase #6	$192.44	3.626%	$199.4179	$199.42	$199.40	$199.40
Purchase #7	$26.56	12.381%	$29.8484	$29.85	$29.85	$29.80
7 purchase totals =	$770.29		$834.8889	$834.89	$834.85	$834.90