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	$246.45	6.632%	$262.7946	$262.79	$262.80	$262.80
Purchase #2	$177.44	10.802%	$196.6071	$196.61	$196.60	$196.60
Purchase #3	$177.32	12.815%	$200.0436	$200.04	$200.05	$200.00
Purchase #4	$140.66	10.822%	$155.8822	$155.88	$155.90	$155.90
Purchase #5	$78.41	8.305%	$84.922	$84.92	$84.90	$84.90
Purchase #6	$93.32	13.731%	$106.1338	$106.13	$106.15	$106.10
Purchase #7	$31.83	3.215%	$32.8533	$32.85	$32.85	$32.90
7 purchase totals =	$945.43		$1,039.2366	$1,039.22	$1,039.25	$1,039.20