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	$9.78	7.222%	$10.4863	$10.49	$10.50	$10.50
Purchase #2	$127.60	12.746%	$143.8639	$143.86	$143.85	$143.90
Purchase #3	$92.93	11.128%	$103.2713	$103.27	$103.25	$103.30
Purchase #4	$215.53	4.680%	$225.6168	$225.62	$225.60	$225.60
Purchase #5	$146.46	7.141%	$156.9187	$156.92	$156.90	$156.90
Purchase #6	$13.41	4.539%	$14.0187	$14.02	$14.00	$14.00
Purchase #7	$32.33	3.341%	$33.4101	$33.41	$33.40	$33.40
7 purchase totals =	$638.04		$687.5858	$687.59	$687.50	$687.60