[Bug Report ID: #1772159437] Ritual deferral discount incorrectly calculated (off by 1)

When a ritual reward's cost is a multiple of 10, the deferral amount may be miscalculated as 1 too low. In the case of this bug report, an Orb of Alchemy was offered at 1100 Tribute, but deferring it shows the future 10% discount as 109 instead of the correct 110. I haven't confirmed whether this error carries over to when the item next appears.

This appears to be a typical floating-point bug, calculating the discount as "cost×0.1" (in this case yielding 109.999..., a value slightly less than 110.0 due to loss of precision) instead of the correct "(cost×10)/100".