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	$40.36	6.536%	$42.9979	$43.00	$43.00	$43.00
Purchase #2	$221.48	11.446%	$246.8306	$246.83	$246.85	$246.80
Purchase #3	$69.61	4.305%	$72.6067	$72.61	$72.60	$72.60
Purchase #4	$208.87	12.575%	$235.1354	$235.14	$235.15	$235.10
Purchase #5	$115.66	5.605%	$122.1427	$122.14	$122.15	$122.10
Purchase #6	$31.42	6.455%	$33.4482	$33.45	$33.45	$33.40
Purchase #7	$72.40	8.670%	$78.6771	$78.68	$78.70	$78.70
7 purchase totals =	$759.80		$831.8386	$831.85	$831.90	$831.70