Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $24.87   8.260%   $26.9243   $26.92   $26.90   $26.90  
  Purchase #2 $57.47   6.723%   $61.3337   $61.33   $61.35   $61.30  
  Purchase #3 $6.45   12.553%   $7.2597   $7.26   $7.25   $7.30  
  Purchase #4 $233.37   11.130%   $259.3441   $259.34   $259.35   $259.30  
  Purchase #5 $250.92   11.805%   $280.5411   $280.54   $280.55   $280.50  
  Purchase #6 $184.43   6.413%   $196.2575   $196.26   $196.25   $196.30  
  Purchase #7 $243.63   13.818%   $277.2948   $277.29   $277.30   $277.30  
  7 purchase totals = $1,001.14       $1,108.9552   $1,108.94   $1,108.95   $1,108.90