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	$41.69	11.793%	$46.6065	$46.61	$46.60	$46.60
Purchase #2	$179.26	6.491%	$190.8958	$190.90	$190.90	$190.90
Purchase #3	$106.84	9.347%	$116.8263	$116.83	$116.85	$116.80
Purchase #4	$239.30	6.773%	$255.5078	$255.51	$255.50	$255.50
Purchase #5	$52.75	10.507%	$58.2924	$58.29	$58.30	$58.30
Purchase #6	$83.29	7.214%	$89.2985	$89.30	$89.30	$89.30
Purchase #7	$83.93	3.371%	$86.7593	$86.76	$86.75	$86.80
7 purchase totals =	$787.06		$844.1866	$844.20	$844.20	$844.20