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	$74.59	10.726%	$82.5905	$82.59	$82.60	$82.60
Purchase #2	$83.29	5.684%	$88.0242	$88.02	$88.00	$88.00
Purchase #3	$86.70	13.102%	$98.0594	$98.06	$98.05	$98.10
Purchase #4	$195.34	13.719%	$222.1387	$222.14	$222.15	$222.10
Purchase #5	$37.71	6.241%	$40.0635	$40.06	$40.05	$40.10
Purchase #6	$28.48	4.840%	$29.8584	$29.86	$29.85	$29.90
Purchase #7	$207.34	8.551%	$225.0696	$225.07	$225.05	$225.10
7 purchase totals =	$713.45		$785.8043	$785.80	$785.75	$785.90