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	$162.43	13.144%	$183.7798	$183.78	$183.80	$183.80
Purchase #2	$230.52	11.856%	$257.8505	$257.85	$257.85	$257.90
Purchase #3	$217.26	4.682%	$227.4321	$227.43	$227.45	$227.40
Purchase #4	$117.39	12.329%	$131.863	$131.86	$131.85	$131.90
Purchase #5	$91.98	12.673%	$103.6366	$103.64	$103.65	$103.60
Purchase #6	$246.37	11.648%	$275.0672	$275.07	$275.05	$275.10
Purchase #7	$121.39	8.204%	$131.3488	$131.35	$131.35	$131.30
7 purchase totals =	$1,187.34		$1,310.9780	$1,310.98	$1,311.00	$1,311.00