Remove code to vibrate on correct answer

Vibrating wasn't working.  Removing the line for now.
Fix bug: Accommodate Cost Value = Bill Value

When the cost value was $1.00 the app said the correct bill was
the $5 bill, etc.

* WBItem's cost property is rounded off to two decimal places when set
* Comparisons are made with 1.005, 5.005, 10.005 instead of with whole numbers.
* Will consider doing away with double calculations and keeping cost in cents.