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	$232.90	12.637%	$262.3316	$262.33	$262.35	$262.30
Purchase #2	$92.50	8.184%	$100.0702	$100.07	$100.05	$100.10
Purchase #3	$199.64	7.856%	$215.3237	$215.32	$215.30	$215.30
Purchase #4	$212.92	4.159%	$221.7753	$221.78	$221.80	$221.80
Purchase #5	$44.56	7.604%	$47.9483	$47.95	$47.95	$47.90
Purchase #6	$28.34	11.449%	$31.5846	$31.58	$31.60	$31.60
Purchase #7	$49.66	4.373%	$51.8316	$51.83	$51.85	$51.80
7 purchase totals =	$860.52		$930.8653	$930.86	$930.90	$930.80