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	$70.91	13.656%	$80.5935	$80.59	$80.60	$80.60
Purchase #2	$120.95	13.487%	$137.2625	$137.26	$137.25	$137.30
Purchase #3	$234.32	4.316%	$244.4333	$244.43	$244.45	$244.40
Purchase #4	$117.51	5.244%	$123.6722	$123.67	$123.65	$123.70
Purchase #5	$50.64	7.868%	$54.6244	$54.62	$54.60	$54.60
Purchase #6	$27.79	9.186%	$30.3428	$30.34	$30.35	$30.30
Purchase #7	$37.55	5.326%	$39.5499	$39.55	$39.55	$39.50
7 purchase totals =	$659.67		$710.4786	$710.46	$710.45	$710.40