"Saving up can be hard, but with an account at Savings 'N' Investments Plus (or SNIP) it's a SNAP! You can put money aside separately so you don't spend it until you're ready. Save up for that perfect weapon, or just keep your cash away from Starbucks!"
Savings 'N' Investments Plus (or SNIP) is a facility in Sector 3 that acts as Mech Crusader's version of a bank. You can store credits in either a regular or interest account at SNIP, the latter working just like it's savings account counterpart in real life.
The interest given works in the following way at SNIP; if your base interest is 0.9%, that only applies for the first 100 million credits in all your interest accounts, but the interest diminishes for the next 100 million credits and so forth (i.e it halves, so if you have 200 million, you gain 0.9% out of the first 100 million, and 0.45% out of the second 100 million).