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	$131.85	3.204%	$136.0745	$136.07	$136.05	$136.10
Purchase #2	$48.61	3.856%	$50.4844	$50.48	$50.50	$50.50
Purchase #3	$218.81	4.105%	$227.7922	$227.79	$227.80	$227.80
Purchase #4	$172.88	9.531%	$189.3572	$189.36	$189.35	$189.40
Purchase #5	$119.67	9.808%	$131.4072	$131.41	$131.40	$131.40
Purchase #6	$153.71	13.764%	$174.8666	$174.87	$174.85	$174.90
Purchase #7	$132.73	10.624%	$146.8312	$146.83	$146.85	$146.80
7 purchase totals =	$978.26		$1,056.8133	$1,056.81	$1,056.80	$1,056.90