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	$43.67	8.788%	$47.5077	$47.51	$47.50	$47.50
Purchase #2	$28.44	13.852%	$32.3795	$32.38	$32.40	$32.40
Purchase #3	$119.90	5.575%	$126.5844	$126.58	$126.60	$126.60
Purchase #4	$85.38	5.832%	$90.3594	$90.36	$90.35	$90.40
Purchase #5	$214.43	13.367%	$243.0929	$243.09	$243.10	$243.10
Purchase #6	$74.70	3.752%	$77.5027	$77.50	$77.50	$77.50
Purchase #7	$148.26	12.553%	$166.8711	$166.87	$166.85	$166.90
7 purchase totals =	$714.78		$784.2977	$784.29	$784.30	$784.40