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	$120.71	10.585%	$133.4872	$133.49	$133.50	$133.50
Purchase #2	$95.68	6.542%	$101.9394	$101.94	$101.95	$101.90
Purchase #3	$90.40	4.584%	$94.5439	$94.54	$94.55	$94.50
Purchase #4	$133.51	7.363%	$143.3403	$143.34	$143.35	$143.30
Purchase #5	$63.60	4.661%	$66.5644	$66.56	$66.55	$66.60
Purchase #6	$139.96	11.134%	$155.5431	$155.54	$155.55	$155.50
Purchase #7	$129.93	10.660%	$143.7805	$143.78	$143.80	$143.80
7 purchase totals =	$773.79		$839.1988	$839.19	$839.25	$839.10