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	$82.37	8.229%	$89.1482	$89.15	$89.15	$89.10
Purchase #2	$182.76	9.359%	$199.8645	$199.86	$199.85	$199.90
Purchase #3	$131.37	11.739%	$146.7915	$146.79	$146.80	$146.80
Purchase #4	$236.59	5.411%	$249.3919	$249.39	$249.40	$249.40
Purchase #5	$20.95	3.830%	$21.7524	$21.75	$21.75	$21.80
Purchase #6	$42.72	4.440%	$44.6168	$44.62	$44.60	$44.60
Purchase #7	$213.27	8.248%	$230.8605	$230.86	$230.85	$230.90
7 purchase totals =	$910.03		$982.4258	$982.42	$982.40	$982.50