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 $76.63   9.241%   $83.7114   $83.71   $83.70   $83.70  
  Purchase #2 $112.87   11.591%   $125.9528   $125.95   $125.95   $126.00  
  Purchase #3 $20.38   8.464%   $22.105   $22.11   $22.10   $22.10  
  Purchase #4 $209.58   11.186%   $233.0236   $233.02   $233.00   $233.00  
  Purchase #5 $163.60   11.818%   $182.9342   $182.93   $182.95   $182.90  
  Purchase #6 $129.88   6.822%   $138.7404   $138.74   $138.75   $138.70  
  Purchase #7 $232.62   3.868%   $241.6177   $241.62   $241.60   $241.60  
  7 purchase totals = $945.56       $1,028.0851   $1,028.08   $1,028.05   $1,028.00