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 $248.58   3.312%   $256.813   $256.81   $256.80   $256.80  
  Purchase #2 $60.29   8.248%   $65.2627   $65.26   $65.25   $65.30  
  Purchase #3 $39.85   8.575%   $43.2671   $43.27   $43.25   $43.30  
  Purchase #4 $44.68   10.145%   $49.2128   $49.21   $49.20   $49.20  
  Purchase #5 $196.40   10.854%   $217.7173   $217.72   $217.70   $217.70  
  Purchase #6 $233.87   12.141%   $262.2642   $262.26   $262.25   $262.30  
  Purchase #7 $144.70   13.434%   $164.139   $164.14   $164.15   $164.10  
  7 purchase totals = $968.37       $1,058.6761   $1,058.67   $1,058.60   $1,058.70