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	$29.65	5.837%	$31.3807	$31.38	$31.40	$31.40
Purchase #2	$95.47	6.794%	$101.9562	$101.96	$101.95	$102.00
Purchase #3	$198.55	3.667%	$205.8308	$205.83	$205.85	$205.80
Purchase #4	$46.85	12.413%	$52.6655	$52.67	$52.65	$52.70
Purchase #5	$123.67	12.313%	$138.8975	$138.90	$138.90	$138.90
Purchase #6	$107.37	11.131%	$119.3214	$119.32	$119.30	$119.30
Purchase #7	$86.44	3.578%	$89.5328	$89.53	$89.55	$89.50
7 purchase totals =	$688.00		$739.5849	$739.59	$739.60	$739.60