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	$233.89	9.110%	$255.1974	$255.20	$255.20	$255.20
Purchase #2	$160.83	7.837%	$173.4342	$173.43	$173.45	$173.40
Purchase #3	$239.43	4.213%	$249.5172	$249.52	$249.50	$249.50
Purchase #4	$43.97	5.528%	$46.4007	$46.40	$46.40	$46.40
Purchase #5	$90.51	5.394%	$95.3921	$95.39	$95.40	$95.40
Purchase #6	$101.94	9.759%	$111.8883	$111.89	$111.90	$111.90
Purchase #7	$126.75	7.179%	$135.8494	$135.85	$135.85	$135.80
7 purchase totals =	$997.32		$1,067.6793	$1,067.68	$1,067.70	$1,067.60