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	$221.66	9.840%	$243.4713	$243.47	$243.45	$243.50
Purchase #2	$110.94	8.108%	$119.935	$119.94	$119.95	$119.90
Purchase #3	$29.92	5.359%	$31.5234	$31.52	$31.50	$31.50
Purchase #4	$20.86	10.389%	$23.0271	$23.03	$23.05	$23.00
Purchase #5	$86.33	4.166%	$89.9265	$89.93	$89.95	$89.90
Purchase #6	$27.27	5.752%	$28.8386	$28.84	$28.85	$28.80
Purchase #7	$83.89	13.733%	$95.4106	$95.41	$95.40	$95.40
7 purchase totals =	$580.87		$632.1325	$632.14	$632.15	$632.00