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	$222.64	8.164%	$240.8163	$240.82	$240.80	$240.80
Purchase #2	$20.93	4.563%	$21.885	$21.89	$21.90	$21.90
Purchase #3	$134.86	3.850%	$140.0521	$140.05	$140.05	$140.10
Purchase #4	$138.95	3.590%	$143.9383	$143.94	$143.95	$143.90
Purchase #5	$40.53	7.268%	$43.4757	$43.48	$43.50	$43.50
Purchase #6	$106.40	10.506%	$117.5784	$117.58	$117.60	$117.60
Purchase #7	$49.93	6.586%	$53.2184	$53.22	$53.20	$53.20
7 purchase totals =	$714.24		$760.9642	$760.98	$761.00	$761.00