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	$82.28	8.146%	$88.9825	$88.98	$89.00	$89.00
Purchase #2	$51.97	13.603%	$59.0395	$59.04	$59.05	$59.00
Purchase #3	$99.61	4.762%	$104.3534	$104.35	$104.35	$104.40
Purchase #4	$109.97	10.606%	$121.6334	$121.63	$121.65	$121.60
Purchase #5	$13.93	9.635%	$15.2722	$15.27	$15.25	$15.30
Purchase #6	$18.58	4.175%	$19.3557	$19.36	$19.35	$19.40
Purchase #7	$114.25	8.388%	$123.8333	$123.83	$123.85	$123.80
7 purchase totals =	$490.59		$532.4700	$532.46	$532.50	$532.50