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	$34.39	11.804%	$38.4494	$38.45	$38.45	$38.40
Purchase #2	$241.27	9.763%	$264.8252	$264.83	$264.85	$264.80
Purchase #3	$62.34	8.299%	$67.5136	$67.51	$67.50	$67.50
Purchase #4	$84.43	13.559%	$95.8779	$95.88	$95.90	$95.90
Purchase #5	$131.39	7.433%	$141.1562	$141.16	$141.15	$141.20
Purchase #6	$240.26	13.213%	$272.0056	$272.01	$272.00	$272.00
Purchase #7	$217.76	3.245%	$224.8263	$224.83	$224.85	$224.80
7 purchase totals =	$1,011.84		$1,104.6542	$1,104.67	$1,104.70	$1,104.60