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	$220.63	11.516%	$246.0378	$246.04	$246.05	$246.00
Purchase #2	$94.65	4.689%	$99.0881	$99.09	$99.10	$99.10
Purchase #3	$161.72	4.186%	$168.4896	$168.49	$168.50	$168.50
Purchase #4	$30.82	11.451%	$34.3492	$34.35	$34.35	$34.30
Purchase #5	$51.46	7.748%	$55.4471	$55.45	$55.45	$55.40
Purchase #6	$179.72	9.597%	$196.9677	$196.97	$196.95	$197.00
Purchase #7	$82.79	9.307%	$90.4953	$90.50	$90.50	$90.50
7 purchase totals =	$821.79		$890.8748	$890.89	$890.90	$890.80