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	$134.79	12.126%	$151.1346	$151.13	$151.15	$151.10
Purchase #2	$59.61	12.208%	$66.8872	$66.89	$66.90	$66.90
Purchase #3	$134.40	12.736%	$151.5172	$151.52	$151.50	$151.50
Purchase #4	$79.81	6.794%	$85.2323	$85.23	$85.25	$85.20
Purchase #5	$199.60	4.458%	$208.4982	$208.50	$208.50	$208.50
Purchase #6	$57.95	3.831%	$60.1701	$60.17	$60.15	$60.20
Purchase #7	$24.40	12.263%	$27.3922	$27.39	$27.40	$27.40
7 purchase totals =	$690.56		$750.8318	$750.83	$750.85	$750.80