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	$87.51	3.268%	$90.3698	$90.37	$90.35	$90.40
Purchase #2	$136.79	5.237%	$143.9537	$143.95	$143.95	$144.00
Purchase #3	$49.39	4.711%	$51.7168	$51.72	$51.70	$51.70
Purchase #4	$48.31	11.557%	$53.8932	$53.89	$53.90	$53.90
Purchase #5	$189.34	12.808%	$213.5907	$213.59	$213.60	$213.60
Purchase #6	$32.32	7.849%	$34.8568	$34.86	$34.85	$34.90
Purchase #7	$249.81	8.673%	$271.476	$271.48	$271.50	$271.50
7 purchase totals =	$793.47		$859.8570	$859.86	$859.85	$860.00