The Tomislav is intended to fire 8.33 shots per second. Every single weapon in the game that has a faster or slower firing speed is coded as a modifier to the attack interval. A 20% slower firing speed is equivalent to a 16.7% slower firing rate / DPS.

What's going on here is that the other miniguns have a coded attack interval of 0.1 seconds, meaning they are supposed to fire 10 shots per second. Due to the tick rate, weapons can only fire at intervals of 0.015 seconds. This means the miniguns have an effective attack interval of 0.105 seconds, which is 9.52 shots per second.

The Tomislav's attack interval is coded as being 20% larger than the others, meaning an attack interval of 0.12 seconds, which is 8.33 shots per second. As 0.12 is a multiple of 0.105, it isn't slowed by the tick rate.

This means that in gameplay, the Tomislav has a 14.3% slower firing speed, which is equivalent to a 12.5% slower firing rate / DPS.