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	$233.76	11.367%	$260.3315	$260.33	$260.35	$260.30
Purchase #2	$46.41	13.159%	$52.5171	$52.52	$52.50	$52.50
Purchase #3	$76.92	11.206%	$85.5397	$85.54	$85.55	$85.50
Purchase #4	$40.60	7.177%	$43.5139	$43.51	$43.50	$43.50
Purchase #5	$9.66	13.673%	$10.9808	$10.98	$11.00	$11.00
Purchase #6	$120.83	5.217%	$127.1337	$127.13	$127.15	$127.10
Purchase #7	$34.99	10.397%	$38.6279	$38.63	$38.65	$38.60
7 purchase totals =	$563.17		$618.6446	$618.64	$618.70	$618.50