"chelseab" wrote:
Can rounded numbers be summed without creating
additional rounding errors?

No. That is why the IRS states (1040 instructions): "If you
have to add two or more amounts to figure the amount to
enter on a line, include cents when adding the amounts and
round off only the total".

Consider values $1.49 and $2.49. If you add then round, you
get $4 (1.49+2.49 = 3.98). If you round first, you get $3
(1+2 = 3).