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	$60.40	9.367%	$66.0577	$66.06	$66.05	$66.10
Purchase #2	$53.97	4.328%	$56.3058	$56.31	$56.30	$56.30
Purchase #3	$48.93	6.228%	$51.9774	$51.98	$52.00	$52.00
Purchase #4	$111.75	11.368%	$124.4537	$124.45	$124.45	$124.50
Purchase #5	$48.89	8.621%	$53.1048	$53.10	$53.10	$53.10
Purchase #6	$10.59	12.591%	$11.9234	$11.92	$11.90	$11.90
Purchase #7	$29.89	4.574%	$31.2572	$31.26	$31.25	$31.30
7 purchase totals =	$364.42		$395.0800	$395.08	$395.05	$395.20