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	$30.57	9.602%	$33.5053	$33.51	$33.50	$33.50
Purchase #2	$45.83	13.193%	$51.8764	$51.88	$51.90	$51.90
Purchase #3	$199.71	11.597%	$222.8704	$222.87	$222.85	$222.90
Purchase #4	$192.87	12.569%	$217.1118	$217.11	$217.10	$217.10
Purchase #5	$75.93	11.389%	$84.5777	$84.58	$84.60	$84.60
Purchase #6	$241.82	13.245%	$273.8491	$273.85	$273.85	$273.80
Purchase #7	$83.88	12.428%	$94.3046	$94.30	$94.30	$94.30
7 purchase totals =	$870.61		$978.0953	$978.10	$978.10	$978.10