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 $98.51   4.732%   $103.1715   $103.17   $103.15   $103.20  
  Purchase #2 $151.48   12.189%   $169.9439   $169.94   $169.95   $169.90  
  Purchase #3 $111.85   5.681%   $118.2042   $118.20   $118.20   $118.20  
  Purchase #4 $93.47   10.833%   $103.5956   $103.60   $103.60   $103.60  
  Purchase #5 $62.72   4.201%   $65.3549   $65.35   $65.35   $65.40  
  Purchase #6 $88.89   8.798%   $96.7105   $96.71   $96.70   $96.70  
  Purchase #7 $249.37   4.737%   $261.1827   $261.18   $261.20   $261.20  
  7 purchase totals = $856.29       $918.1633   $918.15   $918.15   $918.20