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	$243.94	11.755%	$272.6151	$272.62	$272.60	$272.60
Purchase #2	$81.89	5.535%	$86.4226	$86.42	$86.40	$86.40
Purchase #3	$227.34	12.866%	$256.5896	$256.59	$256.60	$256.60
Purchase #4	$117.86	7.507%	$126.7078	$126.71	$126.70	$126.70
Purchase #5	$88.40	8.405%	$95.83	$95.83	$95.85	$95.80
Purchase #6	$236.64	12.362%	$265.8934	$265.89	$265.90	$265.90
Purchase #7	$129.43	10.504%	$143.0253	$143.03	$143.05	$143.00
7 purchase totals =	$1,125.50		$1,247.0838	$1,247.09	$1,247.10	$1,247.00