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	$232.25	10.265%	$256.0905	$256.09	$256.10	$256.10
Purchase #2	$141.71	12.222%	$159.0298	$159.03	$159.05	$159.00
Purchase #3	$76.91	7.380%	$82.586	$82.59	$82.60	$82.60
Purchase #4	$78.63	8.315%	$85.1681	$85.17	$85.15	$85.20
Purchase #5	$144.61	9.191%	$157.9011	$157.90	$157.90	$157.90
Purchase #6	$51.79	10.709%	$57.3362	$57.34	$57.35	$57.30
Purchase #7	$50.72	11.822%	$56.7161	$56.72	$56.70	$56.70
7 purchase totals =	$776.62		$854.8278	$854.84	$854.85	$854.80