A ganged inkjet printhead sealing system maintains inkjet printhead health in an inkjet printing mechanism during periods of printing inactivity. In multi-printhead printing mechanisms, separate caps seal against each of the printheads. The caps each have an outlet vent. The vents are all ganged together and fluidically coupled to a single, common pressure regulation chamber that isolates the environment adjacent the printhead nozzles from the external environment when the printheads are capped. A fluid in a U-shaped manometer tube, or an elastomeric bladder are used to isolate the pressure chamber environment. The bladder may be constructed as a thin-walled sheet, a spring-biased bag, or as a bellows. The pressure chamber volume changes to accommodate pressure spikes during the capping process, as well as environmental changes in temperature, elevation, barometric pressure, etc. An inkjet printing mechanism having such a ganged capping system, along with associated capping methods are also provided.