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	$171.52	3.241%	$177.079	$177.08	$177.10	$177.10
Purchase #2	$240.76	13.845%	$274.0932	$274.09	$274.10	$274.10
Purchase #3	$18.91	10.485%	$20.8927	$20.89	$20.90	$20.90
Purchase #4	$33.97	6.215%	$36.0812	$36.08	$36.10	$36.10
Purchase #5	$52.89	11.652%	$59.0527	$59.05	$59.05	$59.10
Purchase #6	$89.45	6.783%	$95.5174	$95.52	$95.50	$95.50
Purchase #7	$180.72	10.755%	$200.1564	$200.16	$200.15	$200.20
7 purchase totals =	$788.22		$862.8726	$862.87	$862.90	$863.00