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	$96.26	7.195%	$103.1859	$103.19	$103.20	$103.20
Purchase #2	$77.65	10.128%	$85.5144	$85.51	$85.50	$85.50
Purchase #3	$133.55	9.438%	$146.1544	$146.15	$146.15	$146.20
Purchase #4	$250.89	12.595%	$282.4896	$282.49	$282.50	$282.50
Purchase #5	$125.28	9.745%	$137.4885	$137.49	$137.50	$137.50
Purchase #6	$37.77	13.232%	$42.7677	$42.77	$42.75	$42.80
Purchase #7	$95.53	10.756%	$105.8052	$105.81	$105.80	$105.80
7 purchase totals =	$816.93		$903.4057	$903.41	$903.40	$903.50