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	$34.87	13.106%	$39.4401	$39.44	$39.45	$39.40
Purchase #2	$127.29	3.243%	$131.418	$131.42	$131.40	$131.40
Purchase #3	$193.92	3.429%	$200.5695	$200.57	$200.55	$200.60
Purchase #4	$215.40	12.758%	$242.8807	$242.88	$242.90	$242.90
Purchase #5	$101.98	5.859%	$107.955	$107.96	$107.95	$108.00
Purchase #6	$45.38	12.856%	$51.2141	$51.21	$51.20	$51.20
Purchase #7	$216.72	11.588%	$241.8335	$241.83	$241.85	$241.80
7 purchase totals =	$935.56		$1,015.3109	$1,015.31	$1,015.30	$1,015.30