How can I disable all checkboxes on webpage at once?

I have several sets of checkboxes on a webpage. I want to uncheck them all with javascript. Right now, I do it by looking for the names of each set and unchecking them with FOR loops like this...

    for (i=0;i<document.getElementsByName("myboxes").length;i++) {
document.getElementsByName("myboxes")[i].checked=false;}

for (i=0;i<document.getElementsByName("moreboxes").length;i++) {
document.getElementsByName("moreboxes")[i].checked=false;}

for (i=0;i<document.getElementsByName("evenmoreboxes").length;i++) {
document.getElementsByName("evenmoreboxes")[i].checked=false;}

I'm looking for a way to target them all with one loop. I could do getElementsByTagName('input') to target all INPUTS, but that's a problem because I have some radio inputs that I don't want to uncheck. Is there a way to target all checkbox inputs?