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	$79.45	9.596%	$87.074	$87.07	$87.05	$87.10
Purchase #2	$45.40	3.191%	$46.8487	$46.85	$46.85	$46.80
Purchase #3	$149.73	4.490%	$156.4529	$156.45	$156.45	$156.50
Purchase #4	$38.59	11.288%	$42.946	$42.95	$42.95	$42.90
Purchase #5	$56.70	10.841%	$62.8468	$62.85	$62.85	$62.80
Purchase #6	$32.25	7.342%	$34.6178	$34.62	$34.60	$34.60
Purchase #7	$222.62	5.538%	$234.9487	$234.95	$234.95	$234.90
7 purchase totals =	$624.74		$665.7349	$665.74	$665.70	$665.60