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	$11.37	3.630%	$11.7827	$11.78	$11.80	$11.80
Purchase #2	$32.72	6.124%	$34.7238	$34.72	$34.70	$34.70
Purchase #3	$234.50	9.413%	$256.5735	$256.57	$256.55	$256.60
Purchase #4	$164.79	5.340%	$173.5898	$173.59	$173.60	$173.60
Purchase #5	$117.52	5.226%	$123.6616	$123.66	$123.65	$123.70
Purchase #6	$129.60	8.457%	$140.5603	$140.56	$140.55	$140.60
Purchase #7	$41.96	4.830%	$43.9867	$43.99	$44.00	$44.00
7 purchase totals =	$732.46		$784.8784	$784.87	$784.85	$785.00