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	$16.62	5.308%	$17.5022	$17.50	$17.50	$17.50
Purchase #2	$128.89	13.341%	$146.0852	$146.09	$146.10	$146.10
Purchase #3	$171.74	9.115%	$187.3941	$187.39	$187.40	$187.40
Purchase #4	$107.97	8.164%	$116.7847	$116.78	$116.80	$116.80
Purchase #5	$158.56	6.128%	$168.2766	$168.28	$168.30	$168.30
Purchase #6	$10.80	4.506%	$11.2866	$11.29	$11.30	$11.30
Purchase #7	$159.57	4.717%	$167.0969	$167.10	$167.10	$167.10
7 purchase totals =	$754.15		$814.4263	$814.43	$814.50	$814.50