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	$69.65	11.447%	$77.6228	$77.62	$77.60	$77.60
Purchase #2	$129.61	11.509%	$144.5268	$144.53	$144.55	$144.50
Purchase #3	$38.82	4.861%	$40.707	$40.71	$40.70	$40.70
Purchase #4	$113.60	5.165%	$119.4674	$119.47	$119.45	$119.50
Purchase #5	$31.58	4.232%	$32.9165	$32.92	$32.90	$32.90
Purchase #6	$6.72	6.344%	$7.1463	$7.15	$7.15	$7.10
Purchase #7	$55.93	3.555%	$57.9183	$57.92	$57.90	$57.90
7 purchase totals =	$445.91		$480.3051	$480.32	$480.25	$480.20