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	$55.76	6.509%	$59.3894	$59.39	$59.40	$59.40
Purchase #2	$138.27	10.722%	$153.0953	$153.10	$153.10	$153.10
Purchase #3	$121.80	4.873%	$127.7353	$127.74	$127.75	$127.70
Purchase #4	$127.61	12.291%	$143.2945	$143.29	$143.30	$143.30
Purchase #5	$55.41	6.330%	$58.9175	$58.92	$58.90	$58.90
Purchase #6	$61.58	11.552%	$68.6937	$68.69	$68.70	$68.70
Purchase #7	$34.77	13.233%	$39.3711	$39.37	$39.35	$39.40
7 purchase totals =	$595.20		$650.4968	$650.50	$650.50	$650.50