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	$205.99	13.820%	$234.4578	$234.46	$234.45	$234.50
Purchase #2	$134.58	5.544%	$142.0411	$142.04	$142.05	$142.00
Purchase #3	$233.43	11.734%	$260.8207	$260.82	$260.80	$260.80
Purchase #4	$41.51	11.685%	$46.3604	$46.36	$46.35	$46.40
Purchase #5	$157.72	13.535%	$179.0674	$179.07	$179.05	$179.10
Purchase #6	$181.84	4.833%	$190.6283	$190.63	$190.65	$190.60
Purchase #7	$83.82	8.823%	$91.2154	$91.22	$91.20	$91.20
7 purchase totals =	$1,038.89		$1,144.5911	$1,144.60	$1,144.55	$1,144.60