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	$29.48	8.262%	$31.9156	$31.92	$31.90	$31.90
Purchase #2	$45.34	3.484%	$46.9196	$46.92	$46.90	$46.90
Purchase #3	$151.43	5.387%	$159.5875	$159.59	$159.60	$159.60
Purchase #4	$197.66	9.299%	$216.0404	$216.04	$216.05	$216.00
Purchase #5	$134.78	8.422%	$146.1312	$146.13	$146.15	$146.10
Purchase #6	$118.50	13.772%	$134.8198	$134.82	$134.80	$134.80
Purchase #7	$215.47	11.620%	$240.5076	$240.51	$240.50	$240.50
7 purchase totals =	$892.66		$975.9217	$975.93	$975.90	$975.80