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	$23.77	5.353%	$25.0424	$25.04	$25.05	$25.00
Purchase #2	$125.66	12.628%	$141.5283	$141.53	$141.55	$141.50
Purchase #3	$140.51	4.527%	$146.8709	$146.87	$146.85	$146.90
Purchase #4	$88.53	13.168%	$100.1876	$100.19	$100.20	$100.20
Purchase #5	$30.43	6.123%	$32.2932	$32.29	$32.30	$32.30
Purchase #6	$60.25	11.247%	$67.0263	$67.03	$67.05	$67.00
Purchase #7	$135.78	5.709%	$143.5317	$143.53	$143.55	$143.50
7 purchase totals =	$604.93		$656.4804	$656.48	$656.55	$656.40