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	$29.69	7.597%	$31.9455	$31.95	$31.95	$31.90
Purchase #2	$38.55	11.265%	$42.8927	$42.89	$42.90	$42.90
Purchase #3	$92.37	3.116%	$95.2482	$95.25	$95.25	$95.20
Purchase #4	$58.62	11.477%	$65.3478	$65.35	$65.35	$65.30
Purchase #5	$91.44	10.318%	$100.8748	$100.87	$100.85	$100.90
Purchase #6	$57.66	5.132%	$60.6191	$60.62	$60.60	$60.60
Purchase #7	$183.58	3.380%	$189.785	$189.79	$189.80	$189.80
7 purchase totals =	$551.91		$586.7131	$586.72	$586.70	$586.60