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	$80.49	11.721%	$89.9242	$89.92	$89.90	$89.90
Purchase #2	$157.47	12.301%	$176.8404	$176.84	$176.85	$176.80
Purchase #3	$180.69	10.450%	$199.5721	$199.57	$199.55	$199.60
Purchase #4	$45.86	12.104%	$51.4109	$51.41	$51.40	$51.40
Purchase #5	$205.82	13.821%	$234.2664	$234.27	$234.25	$234.30
Purchase #6	$33.85	12.468%	$38.0704	$38.07	$38.05	$38.10
Purchase #7	$127.70	12.761%	$143.9958	$144.00	$144.00	$144.00
7 purchase totals =	$831.88		$934.0802	$934.08	$934.00	$934.10