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	$231.39	3.413%	$239.2873	$239.29	$239.30	$239.30
Purchase #2	$29.43	6.387%	$31.3097	$31.31	$31.30	$31.30
Purchase #3	$109.83	3.706%	$113.9003	$113.90	$113.90	$113.90
Purchase #4	$172.42	13.611%	$195.8881	$195.89	$195.90	$195.90
Purchase #5	$38.91	6.733%	$41.5298	$41.53	$41.55	$41.50
Purchase #6	$83.45	6.704%	$89.0445	$89.04	$89.05	$89.00
Purchase #7	$199.29	9.138%	$217.5011	$217.50	$217.50	$217.50
7 purchase totals =	$864.72		$928.4608	$928.46	$928.50	$928.40