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	$27.46	13.500%	$31.1671	$31.17	$31.15	$31.20
Purchase #2	$43.62	11.442%	$48.611	$48.61	$48.60	$48.60
Purchase #3	$200.32	7.801%	$215.947	$215.95	$215.95	$215.90
Purchase #4	$142.81	6.573%	$152.1969	$152.20	$152.20	$152.20
Purchase #5	$169.93	5.616%	$179.4733	$179.47	$179.45	$179.50
Purchase #6	$134.28	12.365%	$150.8837	$150.88	$150.90	$150.90
Purchase #7	$50.62	3.223%	$52.2515	$52.25	$52.25	$52.30
7 purchase totals =	$769.04		$830.5305	$830.53	$830.50	$830.60