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 $38.71   7.762%   $41.7147   $41.71   $41.70   $41.70  
  Purchase #2 $186.90   5.194%   $196.6076   $196.61   $196.60   $196.60  
  Purchase #3 $170.39   10.514%   $188.3048   $188.30   $188.30   $188.30  
  Purchase #4 $208.70   8.799%   $227.0635   $227.06   $227.05   $227.10  
  Purchase #5 $21.81   9.806%   $23.9487   $23.95   $23.95   $23.90  
  Purchase #6 $208.90   12.457%   $234.9227   $234.92   $234.90   $234.90  
  Purchase #7 $95.30   11.443%   $106.2052   $106.21   $106.20   $106.20  
  7 purchase totals = $930.71       $1,018.7672   $1,018.76   $1,018.70   $1,018.70