When adding non-acidic ingredients to tomatoes it becomes very hard to judge how much more acid is required to make them safe. Since salsa is often not re-heated to boiling before eating, it is very risky to try to can it without pressure cooking - the ONLY way to kill any botulism spoors that may be present. Boiling foods for a certain amount of time will destroy the toxins produced by the Botulism bacteria, but not kill the spoors - which will grow again once the food cools off. Home canning is a great way to eat really good quality food and save money, but in the "old days" many people died from botulism from improperly canned foods. It is not worth the risk to yourself or your family to put up food that may kill you.