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	$164.78	12.614%	$185.5653	$185.57	$185.55	$185.60
Purchase #2	$246.82	7.748%	$265.9436	$265.94	$265.95	$265.90
Purchase #3	$135.98	3.239%	$140.3844	$140.38	$140.40	$140.40
Purchase #4	$137.45	3.743%	$142.5948	$142.59	$142.60	$142.60
Purchase #5	$221.94	8.105%	$239.9282	$239.93	$239.95	$239.90
Purchase #6	$37.47	6.794%	$40.0157	$40.02	$40.00	$40.00
Purchase #7	$22.61	13.434%	$25.6474	$25.65	$25.65	$25.60
7 purchase totals =	$967.05		$1,040.0794	$1,040.08	$1,040.10	$1,040.00