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	$159.75	6.316%	$169.8398	$169.84	$169.85	$169.80
Purchase #2	$85.88	4.703%	$89.9189	$89.92	$89.90	$89.90
Purchase #3	$221.44	7.867%	$238.8607	$238.86	$238.85	$238.90
Purchase #4	$239.70	5.342%	$252.5048	$252.50	$252.50	$252.50
Purchase #5	$53.59	12.329%	$60.1971	$60.20	$60.20	$60.20
Purchase #6	$48.88	10.662%	$54.0916	$54.09	$54.10	$54.10
Purchase #7	$123.92	8.179%	$134.0554	$134.06	$134.05	$134.10
7 purchase totals =	$933.16		$999.4683	$999.47	$999.45	$999.50