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	$38.34	5.844%	$40.5806	$40.58	$40.60	$40.60
Purchase #2	$187.39	5.311%	$197.3423	$197.34	$197.35	$197.30
Purchase #3	$141.42	3.634%	$146.5592	$146.56	$146.55	$146.60
Purchase #4	$155.75	13.344%	$176.5333	$176.53	$176.55	$176.50
Purchase #5	$136.39	4.513%	$142.5453	$142.55	$142.55	$142.50
Purchase #6	$80.59	6.555%	$85.8727	$85.87	$85.85	$85.90
Purchase #7	$29.36	7.770%	$31.6413	$31.64	$31.65	$31.60
7 purchase totals =	$769.24		$821.0747	$821.07	$821.10	$821.00