Decimal Conversion into integer

Dear Experts

i have 1 carton having 15 pieces. suppose i have 12 cartons and i sold 2 cartons and 1 pieces the answer is 10.14 by using the under given formula and i find same result when i added to stock new items i purchase it automatically convert it into carton and pieces as pieces reach to a defined given limit of 15 it automatically converted into a full one carton so i added 3 carton and 2 pieces and after reaching its limit of 15 pieces in a carton it converted .14+.2 into 1 full carton and added into carton side and the remaining 1 single piece is standing alone. this formula is working fine with this carton having 15 pieces but it do not work with carton having 10 pieces or less than 10 pieces. please help me to solve this issue. any formula or vb solution. (kindly remember to increase decimal places atleast up to 2 digits). please also see the attached file for better understanding.

A
1 OPENING STOCK 12.00
2 SOLD 2.01
3 10.14 =DOLLARFR(DOLLARDE(A1,15)-DOLLARDE(A2,15),15)

4 new purchase 3.02
5 closing stock 14.01 =DOLLARFR(DOLLARDE(A3,15)+DOLLARDE(A4,15),15)

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