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	$18.43	9.472%	$20.1757	$20.18	$20.20	$20.20
Purchase #2	$27.85	11.832%	$31.1452	$31.15	$31.15	$31.10
Purchase #3	$201.83	10.434%	$222.8889	$222.89	$222.90	$222.90
Purchase #4	$248.72	13.371%	$281.9764	$281.98	$282.00	$282.00
Purchase #5	$88.69	12.211%	$99.5199	$99.52	$99.50	$99.50
Purchase #6	$138.58	3.405%	$143.2986	$143.30	$143.30	$143.30
Purchase #7	$7.95	11.574%	$8.8701	$8.87	$8.85	$8.90
7 purchase totals =	$732.05		$807.8748	$807.89	$807.90	$807.90