A curious fact about the communication of numerical information is that speakers often choose to use approximate or rounded expressions, even when more precise information is available (for instance, reporting the time as ‘three thirty’ when one’s watch reads 3:27). It has been proposed that this tendency towards rounding is driven by a desire to reduce hearers’ processing costs, a specific claim being that rounded values produce the same cognitive effect at less cognitive effort than non-round values (Van der Henst, Carles and Sperber, 2002). To date, however, the posited processing advantage for roundness has not been experimentally substantiated. Focusing on the domain of temporal expressions, we report on two experiments that demonstrate that rounded clock times are easier to remember and manipulate than their non-round counterparts, a finding that provides evidence for the influence of processing considerations on numerical expression choice. We further find a role for domain-specific granularity of measurement.