The county option income tax (COIT) is 1% for Hamilton County, which includes Carmel. Cities and towns in Indiana do not impose an income tax, counties do (with the exception of Lake). Zionsville is in Boone County, and I'm not familiar with their rate, although this information is probably available at the state's Department of Revenue site (
www.in.gov/dor)
As for property taxes, the reform passed by the General Assembly capped property taxes on homestead properties at 1% of assessed value, starting next year. This can only be raised via local referendum. For now, I believe you're correct to note that property tax rates in Zionsville are a bit higher. Once the caps are fully in effect, however, taxes could still be higher in Zionsville due to higher assessed values.
Indiana's sales tax rate is 7%. Many counties in the Indy metro area assess an additional percent or two on prepared foods (restaurant tax).
Good luck!