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	$90.28	11.347%	$100.5241	$100.52	$100.50	$100.50
Purchase #2	$118.43	8.654%	$128.6789	$128.68	$128.70	$128.70
Purchase #3	$228.64	5.497%	$241.2083	$241.21	$241.20	$241.20
Purchase #4	$85.50	3.349%	$88.3634	$88.36	$88.35	$88.40
Purchase #5	$190.90	4.180%	$198.8796	$198.88	$198.90	$198.90
Purchase #6	$10.90	6.622%	$11.6218	$11.62	$11.60	$11.60
Purchase #7	$89.45	12.366%	$100.5114	$100.51	$100.50	$100.50
7 purchase totals =	$814.10		$869.7875	$869.78	$869.75	$869.80