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	$53.72	12.756%	$60.5725	$60.57	$60.55	$60.60
Purchase #2	$167.81	10.329%	$185.1431	$185.14	$185.15	$185.10
Purchase #3	$176.39	13.529%	$200.2538	$200.25	$200.25	$200.30
Purchase #4	$46.45	9.874%	$51.0365	$51.04	$51.05	$51.00
Purchase #5	$138.88	6.527%	$147.9447	$147.94	$147.95	$147.90
Purchase #6	$83.49	4.626%	$87.3522	$87.35	$87.35	$87.40
Purchase #7	$204.67	8.762%	$222.6032	$222.60	$222.60	$222.60
7 purchase totals =	$871.41		$954.9060	$954.89	$954.90	$954.90