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	$34.28	6.605%	$36.5442	$36.54	$36.55	$36.50
Purchase #2	$239.28	6.756%	$255.4458	$255.45	$255.45	$255.40
Purchase #3	$18.25	8.166%	$19.7403	$19.74	$19.75	$19.70
Purchase #4	$85.54	7.355%	$91.8315	$91.83	$91.85	$91.80
Purchase #5	$26.80	5.434%	$28.2563	$28.26	$28.25	$28.30
Purchase #6	$20.75	5.499%	$21.891	$21.89	$21.90	$21.90
Purchase #7	$173.32	11.273%	$192.8584	$192.86	$192.85	$192.90
7 purchase totals =	$598.22		$646.5675	$646.57	$646.60	$646.50