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	$20.71	4.720%	$21.6875	$21.69	$21.70	$21.70
Purchase #2	$216.51	10.325%	$238.8647	$238.86	$238.85	$238.90
Purchase #3	$90.74	13.826%	$103.2857	$103.29	$103.30	$103.30
Purchase #4	$119.82	5.692%	$126.6402	$126.64	$126.65	$126.60
Purchase #5	$56.81	12.469%	$63.8936	$63.89	$63.90	$63.90
Purchase #6	$35.62	9.173%	$38.8874	$38.89	$38.90	$38.90
Purchase #7	$56.91	12.322%	$63.9225	$63.92	$63.90	$63.90
7 purchase totals =	$597.12		$657.1816	$657.18	$657.20	$657.20