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	$60.47	9.763%	$66.3737	$66.37	$66.35	$66.40
Purchase #2	$139.90	12.168%	$156.923	$156.92	$156.90	$156.90
Purchase #3	$141.60	12.185%	$158.854	$158.85	$158.85	$158.90
Purchase #4	$197.53	11.501%	$220.2479	$220.25	$220.25	$220.20
Purchase #5	$149.63	10.233%	$164.9416	$164.94	$164.95	$164.90
Purchase #6	$111.37	12.832%	$125.661	$125.66	$125.65	$125.70
Purchase #7	$139.85	4.821%	$146.5922	$146.59	$146.60	$146.60
7 purchase totals =	$940.35		$1,039.5934	$1,039.58	$1,039.55	$1,039.60