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	$44.64	6.545%	$47.5617	$47.56	$47.55	$47.60
Purchase #2	$43.55	6.584%	$46.4173	$46.42	$46.40	$46.40
Purchase #3	$208.56	12.479%	$234.5862	$234.59	$234.60	$234.60
Purchase #4	$174.52	12.520%	$196.3699	$196.37	$196.35	$196.40
Purchase #5	$82.33	13.323%	$93.2988	$93.30	$93.30	$93.30
Purchase #6	$87.43	8.436%	$94.8056	$94.81	$94.80	$94.80
Purchase #7	$169.68	4.249%	$176.8897	$176.89	$176.90	$176.90
7 purchase totals =	$810.71		$889.9292	$889.94	$889.90	$890.00