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	$152.25	12.576%	$171.397	$171.40	$171.40	$171.40
Purchase #2	$80.71	11.619%	$90.0877	$90.09	$90.10	$90.10
Purchase #3	$10.43	13.609%	$11.8494	$11.85	$11.85	$11.80
Purchase #4	$33.85	13.637%	$38.4661	$38.47	$38.45	$38.50
Purchase #5	$61.87	3.243%	$63.8764	$63.88	$63.90	$63.90
Purchase #6	$154.89	4.689%	$162.1528	$162.15	$162.15	$162.20
Purchase #7	$50.72	5.659%	$53.5902	$53.59	$53.60	$53.60
7 purchase totals =	$544.72		$591.4196	$591.43	$591.45	$591.50