Colleges are free to process and use scores however they want for intenral admission purposes.
For ranking/reporting purposes, the schools always want to show the highest scores possible. So a 34.6 composite average is always going to be a 35.
Per ACT:
Your Composite score and each test score (English, mathematics, reading, science) range from 1 (low) to 36 (high). The Composite score is the average of your four test scores, rounded to the nearest whole number. Fractions less than one-half are rounded down; fractions one-half or more are rounded up.