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	$229.47	11.483%	$255.82	$255.82	$255.80	$255.80
Purchase #2	$40.90	3.713%	$42.4186	$42.42	$42.40	$42.40
Purchase #3	$47.39	5.223%	$49.8652	$49.87	$49.85	$49.90
Purchase #4	$51.61	3.672%	$53.5051	$53.51	$53.50	$53.50
Purchase #5	$15.46	9.802%	$16.9754	$16.98	$17.00	$17.00
Purchase #6	$174.86	4.733%	$183.1361	$183.14	$183.15	$183.10
Purchase #7	$234.92	8.499%	$254.8859	$254.89	$254.90	$254.90
7 purchase totals =	$794.61		$856.6063	$856.63	$856.60	$856.60