For the only math I found, I wrote a little program on my HP11c/HP41cx. You enter the base price of a material, press ENTER and then type in the total sum of percentage modification. "PRG A" gives you the rounded up result of the total value of your product. Example: 7, ENTER, 60, LBL A. Output: 12
LBL A
%
+
.99
+
INT
RTN
They used a HP41 as a manual board computer in the space shuttle. Very authentic experience :)