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	$150.76	4.340%	$157.303	$157.30	$157.30	$157.30
Purchase #2	$246.76	13.116%	$279.125	$279.13	$279.15	$279.10
Purchase #3	$126.98	3.577%	$131.5221	$131.52	$131.50	$131.50
Purchase #4	$203.74	6.733%	$217.4578	$217.46	$217.45	$217.50
Purchase #5	$180.78	4.453%	$188.8301	$188.83	$188.85	$188.80
Purchase #6	$81.86	9.290%	$89.4648	$89.46	$89.45	$89.50
Purchase #7	$7.26	6.453%	$7.7285	$7.73	$7.75	$7.70
7 purchase totals =	$998.14		$1,071.4313	$1,071.43	$1,071.45	$1,071.40