"Sin" is a subjective term, usually with theological implications. As an atheist with a materialistic/naturalistic world view, my objective morality demands what is fair to myself and others. I accept taxes as the cost of living in civilized community in my town, county, state, and the USA, with all the individual rights, democratic freedoms, and services I derive therefrom.
When a citizen fails to pay what is fairly owed under the laws of the various tax jurisdictions, he or she "steals" from all the rest of citizens who pay. All revenues not collected, of necessity, raise rates and/or reduce the level of services for everyone else.