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	$63.95	11.382%	$71.2288	$71.23	$71.25	$71.20
Purchase #2	$71.70	12.659%	$80.7765	$80.78	$80.80	$80.80
Purchase #3	$223.53	12.509%	$251.4914	$251.49	$251.50	$251.50
Purchase #4	$77.38	6.507%	$82.4151	$82.42	$82.40	$82.40
Purchase #5	$34.40	8.463%	$37.3113	$37.31	$37.30	$37.30
Purchase #6	$95.67	6.204%	$101.6054	$101.61	$101.60	$101.60
Purchase #7	$23.97	6.842%	$25.61	$25.61	$25.60	$25.60
7 purchase totals =	$590.60		$650.4385	$650.45	$650.45	$650.40