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	$127.63	12.490%	$143.571	$143.57	$143.55	$143.60
Purchase #2	$134.63	13.823%	$153.2399	$153.24	$153.25	$153.20
Purchase #3	$105.74	6.737%	$112.8637	$112.86	$112.85	$112.90
Purchase #4	$9.72	5.496%	$10.2542	$10.25	$10.25	$10.30
Purchase #5	$179.84	8.576%	$195.2631	$195.26	$195.25	$195.30
Purchase #6	$125.96	10.766%	$139.5209	$139.52	$139.50	$139.50
Purchase #7	$90.78	8.634%	$98.6179	$98.62	$98.60	$98.60
7 purchase totals =	$774.30		$853.3307	$853.32	$853.25	$853.40