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	$235.68	8.577%	$255.8943	$255.89	$255.90	$255.90
Purchase #2	$42.77	10.643%	$47.322	$47.32	$47.30	$47.30
Purchase #3	$132.77	5.792%	$140.46	$140.46	$140.45	$140.50
Purchase #4	$140.37	9.174%	$153.2475	$153.25	$153.25	$153.20
Purchase #5	$16.89	5.414%	$17.8044	$17.80	$17.80	$17.80
Purchase #6	$171.43	11.575%	$191.273	$191.27	$191.25	$191.30
Purchase #7	$117.51	4.732%	$123.0706	$123.07	$123.05	$123.10
7 purchase totals =	$857.42		$929.0718	$929.06	$929.00	$929.10