Actually, no, it won't.
DDO is not based on a d20 combat system. That is, a "-5 penalty" is not a -5 penalty to a d20 roll (which would be about -25% to hit!). It's a far more convoluted formula, and ends up being ~about~ a -1 to hit, and then ONLY if you do not have a well-designed build (i.e. your total "to hit" bonuses are shaky to start with).
Most well-designed (and geared) characters have more than enough Total Attack Bonus that they'll never feel that -5, and still only miss on a natural 1.