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	$87.62	3.580%	$90.7568	$90.76	$90.75	$90.80
Purchase #2	$158.67	7.412%	$170.4306	$170.43	$170.45	$170.40
Purchase #3	$148.72	4.527%	$155.4526	$155.45	$155.45	$155.50
Purchase #4	$105.84	10.200%	$116.6357	$116.64	$116.65	$116.60
Purchase #5	$38.69	3.700%	$40.1215	$40.12	$40.10	$40.10
Purchase #6	$32.49	5.639%	$34.3221	$34.32	$34.30	$34.30
Purchase #7	$91.70	13.207%	$103.8108	$103.81	$103.80	$103.80
7 purchase totals =	$663.73		$711.5301	$711.53	$711.50	$711.50