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	$96.78	9.342%	$105.8212	$105.82	$105.80	$105.80
Purchase #2	$55.85	13.363%	$63.3132	$63.31	$63.30	$63.30
Purchase #3	$143.39	5.759%	$151.6478	$151.65	$151.65	$151.60
Purchase #4	$27.34	3.790%	$28.3762	$28.38	$28.40	$28.40
Purchase #5	$40.97	7.855%	$44.1882	$44.19	$44.20	$44.20
Purchase #6	$42.42	11.821%	$47.4345	$47.43	$47.45	$47.40
Purchase #7	$175.84	13.622%	$199.7929	$199.79	$199.80	$199.80
7 purchase totals =	$582.59		$640.5740	$640.57	$640.60	$640.50