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	$116.68	9.103%	$127.3014	$127.30	$127.30	$127.30
Purchase #2	$135.57	6.106%	$143.8479	$143.85	$143.85	$143.80
Purchase #3	$14.48	9.787%	$15.8972	$15.90	$15.90	$15.90
Purchase #4	$111.59	11.732%	$124.6817	$124.68	$124.70	$124.70
Purchase #5	$55.25	12.159%	$61.9678	$61.97	$61.95	$62.00
Purchase #6	$154.94	10.660%	$171.4566	$171.46	$171.45	$171.50
Purchase #7	$26.59	11.292%	$29.5925	$29.59	$29.60	$29.60
7 purchase totals =	$615.10		$674.7451	$674.75	$674.75	$674.80