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	$206.61	12.230%	$231.8784	$231.88	$231.90	$231.90
Purchase #2	$30.50	12.602%	$34.3436	$34.34	$34.35	$34.30
Purchase #3	$209.95	8.526%	$227.8503	$227.85	$227.85	$227.90
Purchase #4	$12.94	6.292%	$13.7542	$13.75	$13.75	$13.80
Purchase #5	$52.33	12.745%	$58.9995	$59.00	$59.00	$59.00
Purchase #6	$42.45	7.394%	$45.5888	$45.59	$45.60	$45.60
Purchase #7	$226.54	13.636%	$257.431	$257.43	$257.45	$257.40
7 purchase totals =	$781.32		$869.8458	$869.84	$869.90	$869.90