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	$58.42	9.518%	$63.9804	$63.98	$64.00	$64.00
Purchase #2	$246.86	4.591%	$258.1933	$258.19	$258.20	$258.20
Purchase #3	$19.65	10.114%	$21.6374	$21.64	$21.65	$21.60
Purchase #4	$72.80	5.201%	$76.5863	$76.59	$76.60	$76.60
Purchase #5	$38.38	9.589%	$42.0603	$42.06	$42.05	$42.10
Purchase #6	$183.28	4.119%	$190.8293	$190.83	$190.85	$190.80
Purchase #7	$36.50	9.531%	$39.9788	$39.98	$40.00	$40.00
7 purchase totals =	$655.89		$693.2658	$693.27	$693.35	$693.30