Question about taxes/capital gains in SGOV

Hi all, Long story short I have been looking for somewhere to park my emergency fund rather than let it sit in a regular savings account gaining no interest. Ive been doing some research on SGOV and specifically through fidelity as I already have a Roth IRA there. I understand that SGOV is state tax free and will pay dividends monthly which is the only taxable amount come tax season. My question is this: Say I buy $10,000 of SGOV at $100.00 per share and then set them to auto buy again when they mature at the end of the month. When they mature lets say at $100.30 after the month do you pay capital gains taxes on that as well? I understand it would not add up to much come tax season but I want to fully understand before I park my money there. Thank you for any help!