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	$71.49	12.609%	$80.5042	$80.50	$80.50	$80.50
Purchase #2	$154.78	12.747%	$174.5098	$174.51	$174.50	$174.50
Purchase #3	$131.88	11.383%	$146.8919	$146.89	$146.90	$146.90
Purchase #4	$32.72	6.228%	$34.7578	$34.76	$34.75	$34.80
Purchase #5	$91.26	9.663%	$100.0785	$100.08	$100.10	$100.10
Purchase #6	$109.57	4.784%	$114.8118	$114.81	$114.80	$114.80
Purchase #7	$234.93	10.181%	$258.8482	$258.85	$258.85	$258.80
7 purchase totals =	$826.63		$910.4022	$910.40	$910.40	$910.40