price - (1/4)×price = price×(1 - 1/4) = (3/4)×price
... = (3/4)×5.90 = 4.425 ≈ 4.43 . . . . . sale price
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The sale price could be 4.42 if the discount is rounded up, rather than the price being rounded up. If you first compute the discount as (1/4)×5.90 = 1.475 ≈ 1.48, then the half-penny goes to the customer, not the shop-keeper.