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	$204.49	13.240%	$231.5645	$231.56	$231.55	$231.60
Purchase #2	$111.35	5.528%	$117.5054	$117.51	$117.50	$117.50
Purchase #3	$89.65	10.570%	$99.126	$99.13	$99.15	$99.10
Purchase #4	$28.80	10.631%	$31.8617	$31.86	$31.85	$31.90
Purchase #5	$60.48	3.431%	$62.5551	$62.56	$62.55	$62.60
Purchase #6	$59.30	12.665%	$66.8103	$66.81	$66.80	$66.80
Purchase #7	$63.38	8.390%	$68.6976	$68.70	$68.70	$68.70
7 purchase totals =	$617.45		$678.1206	$678.13	$678.10	$678.20