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	$8.79	5.861%	$9.3052	$9.31	$9.30	$9.30
Purchase #2	$242.41	5.248%	$255.1317	$255.13	$255.15	$255.10
Purchase #3	$84.39	12.659%	$95.0729	$95.07	$95.05	$95.10
Purchase #4	$50.36	5.337%	$53.0477	$53.05	$53.05	$53.00
Purchase #5	$85.83	4.385%	$89.5936	$89.59	$89.60	$89.60
Purchase #6	$40.84	6.318%	$43.4203	$43.42	$43.40	$43.40
Purchase #7	$126.72	6.509%	$134.9682	$134.97	$134.95	$135.00
7 purchase totals =	$639.34		$680.5396	$680.54	$680.50	$680.50