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	$62.88	3.229%	$64.9104	$64.91	$64.90	$64.90
Purchase #2	$103.94	4.660%	$108.7836	$108.78	$108.80	$108.80
Purchase #3	$41.61	12.288%	$46.723	$46.72	$46.70	$46.70
Purchase #4	$233.61	6.788%	$249.4674	$249.47	$249.45	$249.50
Purchase #5	$132.40	10.189%	$145.8902	$145.89	$145.90	$145.90
Purchase #6	$78.74	9.138%	$85.9353	$85.94	$85.95	$85.90
Purchase #7	$122.77	11.475%	$136.8579	$136.86	$136.85	$136.90
7 purchase totals =	$775.95		$838.5678	$838.57	$838.55	$838.60