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	$247.29	3.321%	$255.5025	$255.50	$255.50	$255.50
Purchase #2	$117.81	12.769%	$132.8532	$132.85	$132.85	$132.90
Purchase #3	$215.78	10.624%	$238.7045	$238.70	$238.70	$238.70
Purchase #4	$47.33	8.649%	$51.4236	$51.42	$51.40	$51.40
Purchase #5	$116.45	13.203%	$131.8249	$131.82	$131.80	$131.80
Purchase #6	$18.28	12.141%	$20.4994	$20.50	$20.50	$20.50
Purchase #7	$139.32	5.457%	$146.9227	$146.92	$146.90	$146.90
7 purchase totals =	$902.26		$977.7308	$977.71	$977.65	$977.70