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	$104.65	6.520%	$111.4732	$111.47	$111.45	$111.50
Purchase #2	$190.45	13.142%	$215.4789	$215.48	$215.50	$215.50
Purchase #3	$7.80	8.461%	$8.46	$8.46	$8.45	$8.50
Purchase #4	$205.82	3.253%	$212.5153	$212.52	$212.50	$212.50
Purchase #5	$55.71	13.822%	$63.4102	$63.41	$63.40	$63.40
Purchase #6	$94.52	12.452%	$106.2896	$106.29	$106.30	$106.30
Purchase #7	$146.66	11.117%	$162.9642	$162.96	$162.95	$163.00
7 purchase totals =	$805.61		$880.5914	$880.59	$880.55	$880.70