The SLICE REFINER plugin allows to create round corners & soft edges for slices. 

Just Drag your slices to the Drop-Zone, configure the roundness, and add a stroke.
Use the Equal-Corners option to apply the same roundness to all slices.
Use the soft edges slider to soften the slices edges.
Four slice-groups can help achieve different roundness settings to separate collection of slices. 

New for version 2.0:
Merge Mode – It is now possible to merge Slices to create new looks!
Effects Panel – The Plugin contains built in Visual Slice Effects.
Effects can be colorized using two user defined colors.
Rough & Smooth modes are also selectable.
New Stroke looks – Dual Edge and Color Cycles effects can be combined with all other effects.
Frame Bounce – Add some craziness to the slice’s edges by using a speed slider or by the composition’s BPM.

Compatible with Resolume Arena 7.14.2 and above.

The Plugin Supports Square slices.
Soft Edge & Frame Bounce are “Per Slice” effects
Performance of a high number of slices depends on GPU power.

Notice to Version 1.0 owners!
SLICE REFINER is now being handled by the Juicebar Team.
Although this is a major update, I have decided to give it for FREE! to previous owners.
An email with a special redeem link has been sent to the original email address used to purchase the addon.