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	$166.89	9.406%	$182.5877	$182.59	$182.60	$182.60
Purchase #2	$213.42	3.798%	$221.5257	$221.53	$221.55	$221.50
Purchase #3	$109.29	7.287%	$117.254	$117.25	$117.25	$117.30
Purchase #4	$82.89	7.298%	$88.9393	$88.94	$88.95	$88.90
Purchase #5	$34.83	8.693%	$37.8578	$37.86	$37.85	$37.90
Purchase #6	$119.78	4.725%	$125.4396	$125.44	$125.45	$125.40
Purchase #7	$205.58	9.340%	$224.7812	$224.78	$224.80	$224.80
7 purchase totals =	$932.68		$998.3853	$998.39	$998.45	$998.40