Having done over 35 different financing rounds over 7 companies I've built in Silicon Valley - you should be giving up 15%-25% dilution in each round with a plan to never raise beyond a Series-C.

Investors get equity for money invested, don't start doing "special deals" or it could poison the well for future investors. If you want to "slightly" sweeten it for a truly early investor , then put them on your advisory board for 1/4 a point equity ( vesting over 2 years). Then they have to deliver some value for that equity.

-MD