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	$13.37	11.368%	$14.8899	$14.89	$14.90	$14.90
Purchase #2	$52.33	5.294%	$55.1004	$55.10	$55.10	$55.10
Purchase #3	$192.85	6.680%	$205.7324	$205.73	$205.75	$205.70
Purchase #4	$6.93	5.677%	$7.3234	$7.32	$7.30	$7.30
Purchase #5	$58.62	13.557%	$66.5671	$66.57	$66.55	$66.60
Purchase #6	$223.92	7.829%	$241.4507	$241.45	$241.45	$241.50
Purchase #7	$76.58	12.191%	$85.9159	$85.92	$85.90	$85.90
7 purchase totals =	$624.60		$676.9798	$676.98	$676.95	$677.00