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	$87.34	3.587%	$90.4729	$90.47	$90.45	$90.50
Purchase #2	$217.93	10.320%	$240.4204	$240.42	$240.40	$240.40
Purchase #3	$48.84	3.531%	$50.5645	$50.56	$50.55	$50.60
Purchase #4	$90.51	13.535%	$102.7605	$102.76	$102.75	$102.80
Purchase #5	$187.49	4.673%	$196.2514	$196.25	$196.25	$196.30
Purchase #6	$92.94	9.859%	$102.103	$102.10	$102.10	$102.10
Purchase #7	$173.91	7.808%	$187.4889	$187.49	$187.50	$187.50
7 purchase totals =	$898.96		$970.0616	$970.05	$970.00	$970.20