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	$60.34	11.710%	$67.4058	$67.41	$67.40	$67.40
Purchase #2	$159.63	5.593%	$168.5581	$168.56	$168.55	$168.60
Purchase #3	$71.27	4.709%	$74.6261	$74.63	$74.65	$74.60
Purchase #4	$37.90	13.118%	$42.8717	$42.87	$42.85	$42.90
Purchase #5	$129.65	12.524%	$145.8874	$145.89	$145.90	$145.90
Purchase #6	$17.60	10.863%	$19.5119	$19.51	$19.50	$19.50
Purchase #7	$34.40	12.874%	$38.8287	$38.83	$38.85	$38.80
7 purchase totals =	$510.79		$557.6897	$557.70	$557.70	$557.70