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	$28.45	12.171%	$31.9126	$31.91	$31.90	$31.90
Purchase #2	$94.86	9.401%	$103.7778	$103.78	$103.80	$103.80
Purchase #3	$18.86	5.328%	$19.8649	$19.86	$19.85	$19.90
Purchase #4	$50.49	13.595%	$57.3541	$57.35	$57.35	$57.40
Purchase #5	$155.77	9.653%	$170.8065	$170.81	$170.80	$170.80
Purchase #6	$206.55	7.585%	$222.2168	$222.22	$222.20	$222.20
Purchase #7	$12.54	8.770%	$13.6398	$13.64	$13.65	$13.60
7 purchase totals =	$567.52		$619.5725	$619.57	$619.55	$619.60