Is it permissible, from a Sharia perspective, not to be concerned with the issue of taxes imposed on software sales in regions where the law does not obligate the selling company to collect and transfer them to the competent authorities?

Some taxes are forbidden, and some are permissible. If they are forbidden, then it is permissible to evade them, and one is not bound to fulfill the condition related to them due to its invalidity in Islamic law. However, if they are permissible, then the default is that one is bound to fulfill the condition related to them, for whoever is able, due to the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions."