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	$62.62	6.372%	$66.6101	$66.61	$66.60	$66.60
Purchase #2	$55.53	6.312%	$59.0351	$59.04	$59.05	$59.00
Purchase #3	$127.88	13.776%	$145.4967	$145.50	$145.50	$145.50
Purchase #4	$83.80	10.470%	$92.5739	$92.57	$92.55	$92.60
Purchase #5	$70.32	7.467%	$75.5708	$75.57	$75.55	$75.60
Purchase #6	$144.64	6.683%	$154.3063	$154.31	$154.30	$154.30
Purchase #7	$199.77	12.255%	$224.2518	$224.25	$224.25	$224.30
7 purchase totals =	$744.56		$817.8447	$817.85	$817.80	$817.90