I set mine up on a county level then if you have to collect an additional for a particular city then you would set the city tax on its own. So for me I have Los Angeles county so I chose zipcode as the basis for the sales tax then in the delimited list I put something like this (this is only a fraction of the zipcode but you get the idea):

90001;90002;90003;90004;90005;90006;90007;90008;90009;90010;90011;90012;90013;90 014;90015;90016;90017;90018;90019;90020;90021;90022;90023;90024;90025;90026;9002 7;90028;90029;90030;90031;90032;90033;90034;90035;
Then I put the county tax rate of 1.50

If you have to collect an addition amount for a particular city then you would set this particular city as its own - but make sure the zipcodes for this city is in the county level too! That way they add together to get the correct amount.

So then it would display the county tax then under it would be the city tax.

This worked for me!

Hope this helps.