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	$82.42	9.531%	$90.2755	$90.28	$90.30	$90.30
Purchase #2	$34.96	7.657%	$37.6369	$37.64	$37.65	$37.60
Purchase #3	$115.88	6.488%	$123.3983	$123.40	$123.40	$123.40
Purchase #4	$16.39	6.776%	$17.5006	$17.50	$17.50	$17.50
Purchase #5	$44.93	3.748%	$46.614	$46.61	$46.60	$46.60
Purchase #6	$162.42	9.479%	$177.8158	$177.82	$177.80	$177.80
Purchase #7	$126.87	8.343%	$137.4548	$137.45	$137.45	$137.50
7 purchase totals =	$583.87		$630.6959	$630.70	$630.70	$630.70