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	$40.69	3.250%	$42.0124	$42.01	$42.00	$42.00
Purchase #2	$116.94	5.682%	$123.5845	$123.58	$123.60	$123.60
Purchase #3	$155.55	13.560%	$176.6426	$176.64	$176.65	$176.60
Purchase #4	$98.60	9.780%	$108.2431	$108.24	$108.25	$108.20
Purchase #5	$20.97	7.135%	$22.4662	$22.47	$22.45	$22.50
Purchase #6	$99.62	4.179%	$103.7831	$103.78	$103.80	$103.80
Purchase #7	$99.81	13.461%	$113.2454	$113.25	$113.25	$113.20
7 purchase totals =	$632.18		$689.9773	$689.97	$690.00	$689.90