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	$37.72	11.697%	$42.1321	$42.13	$42.15	$42.10
Purchase #2	$65.81	10.351%	$72.622	$72.62	$72.60	$72.60
Purchase #3	$176.75	4.739%	$185.1262	$185.13	$185.15	$185.10
Purchase #4	$12.25	12.538%	$13.7859	$13.79	$13.80	$13.80
Purchase #5	$93.31	12.350%	$104.8338	$104.83	$104.85	$104.80
Purchase #6	$98.60	5.408%	$103.9323	$103.93	$103.95	$103.90
Purchase #7	$24.57	12.767%	$27.7069	$27.71	$27.70	$27.70
7 purchase totals =	$509.01		$550.1392	$550.14	$550.20	$550.00