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	$76.87	9.406%	$84.1004	$84.10	$84.10	$84.10
Purchase #2	$111.45	11.499%	$124.2656	$124.27	$124.25	$124.30
Purchase #3	$112.62	9.554%	$123.3797	$123.38	$123.40	$123.40
Purchase #4	$224.71	7.164%	$240.8082	$240.81	$240.80	$240.80
Purchase #5	$237.98	3.124%	$245.4145	$245.41	$245.40	$245.40
Purchase #6	$90.94	10.528%	$100.5142	$100.51	$100.50	$100.50
Purchase #7	$59.79	10.433%	$66.0279	$66.03	$66.05	$66.00
7 purchase totals =	$914.36		$984.5105	$984.51	$984.50	$984.50