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	$81.67	10.286%	$90.0706	$90.07	$90.05	$90.10
Purchase #2	$68.32	8.132%	$73.8758	$73.88	$73.90	$73.90
Purchase #3	$61.82	7.748%	$66.6098	$66.61	$66.60	$66.60
Purchase #4	$78.54	8.826%	$85.4719	$85.47	$85.45	$85.50
Purchase #5	$132.87	10.558%	$146.8984	$146.90	$146.90	$146.90
Purchase #6	$27.73	11.606%	$30.9483	$30.95	$30.95	$30.90
Purchase #7	$131.77	4.853%	$138.1648	$138.16	$138.15	$138.20
7 purchase totals =	$582.72		$632.0396	$632.04	$632.00	$632.10