Rounding rules for interest calculation standardize period and amount determination under income tax provisions for accrual. Calculation of interest under the Income-tax Rules uses prescribed rounding conventions: annual periods are rounded down to whole months while month-by-month calculations treat any fractional month as a full month, and the tax, penalty or other sum on which interest is computed is rounded to the nearest prescribed currency multiple with fractional units ignored; the rounded period and amount are the operative inputs for interest computation.