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	$234.92	13.601%	$266.8715	$266.87	$266.85	$266.90
Purchase #2	$13.80	12.406%	$15.512	$15.51	$15.50	$15.50
Purchase #3	$81.87	10.737%	$90.6604	$90.66	$90.65	$90.70
Purchase #4	$244.83	13.105%	$276.915	$276.92	$276.90	$276.90
Purchase #5	$41.61	3.869%	$43.2199	$43.22	$43.20	$43.20
Purchase #6	$70.77	13.156%	$80.0805	$80.08	$80.10	$80.10
Purchase #7	$34.99	8.374%	$37.9201	$37.92	$37.90	$37.90
7 purchase totals =	$722.79		$811.1794	$811.18	$811.10	$811.20