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	$156.46	9.106%	$170.7072	$170.71	$170.70	$170.70
Purchase #2	$162.49	10.547%	$179.6278	$179.63	$179.65	$179.60
Purchase #3	$34.62	7.661%	$37.2722	$37.27	$37.25	$37.30
Purchase #4	$206.25	4.326%	$215.1724	$215.17	$215.15	$215.20
Purchase #5	$97.47	3.548%	$100.9282	$100.93	$100.95	$100.90
Purchase #6	$229.54	12.768%	$258.8477	$258.85	$258.85	$258.80
Purchase #7	$18.94	13.868%	$21.5666	$21.57	$21.55	$21.60
7 purchase totals =	$905.77		$984.1221	$984.13	$984.10	$984.10