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	$83.75	7.443%	$89.9835	$89.98	$90.00	$90.00
Purchase #2	$6.29	4.734%	$6.5878	$6.59	$6.60	$6.60
Purchase #3	$19.47	11.595%	$21.7275	$21.73	$21.75	$21.70
Purchase #4	$139.91	11.691%	$156.2669	$156.27	$156.25	$156.30
Purchase #5	$75.95	13.741%	$86.3863	$86.39	$86.40	$86.40
Purchase #6	$236.37	5.128%	$248.4911	$248.49	$248.50	$248.50
Purchase #7	$14.45	6.744%	$15.4245	$15.42	$15.40	$15.40
7 purchase totals =	$576.19		$624.8676	$624.87	$624.90	$624.90