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	$18.48	3.797%	$19.1817	$19.18	$19.20	$19.20
Purchase #2	$205.72	5.710%	$217.4666	$217.47	$217.45	$217.50
Purchase #3	$81.69	4.691%	$85.5221	$85.52	$85.50	$85.50
Purchase #4	$37.46	12.739%	$42.232	$42.23	$42.25	$42.20
Purchase #5	$64.51	3.571%	$66.8137	$66.81	$66.80	$66.80
Purchase #6	$139.98	3.688%	$145.1425	$145.14	$145.15	$145.10
Purchase #7	$228.42	8.342%	$247.4748	$247.47	$247.45	$247.50
7 purchase totals =	$776.26		$823.8334	$823.82	$823.80	$823.80