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	$87.45	13.410%	$99.177	$99.18	$99.20	$99.20
Purchase #2	$100.84	4.804%	$105.6844	$105.68	$105.70	$105.70
Purchase #3	$16.79	5.869%	$17.7754	$17.78	$17.80	$17.80
Purchase #4	$15.98	6.369%	$16.9978	$17.00	$17.00	$17.00
Purchase #5	$241.83	5.808%	$255.8755	$255.88	$255.90	$255.90
Purchase #6	$51.53	13.557%	$58.5159	$58.52	$58.50	$58.50
Purchase #7	$100.53	12.656%	$113.2531	$113.25	$113.25	$113.30
7 purchase totals =	$614.95		$667.2791	$667.29	$667.35	$667.40