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	$204.44	9.638%	$224.1439	$224.14	$224.15	$224.10
Purchase #2	$39.91	12.821%	$45.0269	$45.03	$45.05	$45.00
Purchase #3	$41.87	3.590%	$43.3731	$43.37	$43.35	$43.40
Purchase #4	$29.45	10.358%	$32.5004	$32.50	$32.50	$32.50
Purchase #5	$72.60	8.568%	$78.8204	$78.82	$78.80	$78.80
Purchase #6	$187.87	6.395%	$199.8843	$199.88	$199.90	$199.90
Purchase #7	$180.89	3.418%	$187.0728	$187.07	$187.05	$187.10
7 purchase totals =	$757.03		$810.8218	$810.81	$810.80	$810.80