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	$165.89	11.798%	$185.4617	$185.46	$185.45	$185.50
Purchase #2	$106.93	5.210%	$112.5011	$112.50	$112.50	$112.50
Purchase #3	$143.60	11.855%	$160.6238	$160.62	$160.60	$160.60
Purchase #4	$31.45	9.777%	$34.5249	$34.52	$34.50	$34.50
Purchase #5	$172.47	4.453%	$180.1501	$180.15	$180.15	$180.20
Purchase #6	$177.31	4.177%	$184.7162	$184.72	$184.70	$184.70
Purchase #7	$206.29	7.412%	$221.5802	$221.58	$221.60	$221.60
7 purchase totals =	$1,003.94		$1,079.5580	$1,079.55	$1,079.50	$1,079.60