The Cambridge dictionary entry is incomplete because it only addresses "used to." The basic rule is that after an unvoiced consonant, -ed is pronounced [t] and after a voiced consonant or a vowel, -ed is pronounced as [d]. Thus "used" is normally pronounced [juzd] as in the phrase "I used a hammer." However, in the expression "used to do," the [zd] sounds before "to" change their pronounciation to [st]. Thus "used to" is not pronounced as [juzdtoʊ] but instead as [justtoʊ] as in the phrase "I used to have a car." When said normally, [justtoʊ] reduces to [justoʊ]. A similar change occurs for "have to do." Thus "have" is pronounced [hæv] in "I have a car" and [hæf] in "I have to take the car to work."

pronounces as something like "use der" as a single sound.