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	$39.42	4.705%	$41.2747	$41.27	$41.25	$41.30
Purchase #2	$217.28	11.863%	$243.0559	$243.06	$243.05	$243.10
Purchase #3	$198.98	7.726%	$214.3532	$214.35	$214.35	$214.40
Purchase #4	$84.39	6.178%	$89.6036	$89.60	$89.60	$89.60
Purchase #5	$146.35	4.257%	$152.5801	$152.58	$152.60	$152.60
Purchase #6	$111.65	4.622%	$116.8105	$116.81	$116.80	$116.80
Purchase #7	$31.52	10.565%	$34.8501	$34.85	$34.85	$34.90
7 purchase totals =	$829.59		$892.5281	$892.52	$892.50	$892.70