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 $137.59   8.830%   $149.7392   $149.74   $149.75   $149.70  
  Purchase #2 $233.88   10.867%   $259.2957   $259.30   $259.30   $259.30  
  Purchase #3 $61.62   8.515%   $66.8669   $66.87   $66.85   $66.90  
  Purchase #4 $118.99   3.257%   $122.8655   $122.87   $122.85   $122.90  
  Purchase #5 $30.63   10.111%   $33.727   $33.73   $33.75   $33.70  
  Purchase #6 $73.41   3.533%   $76.0036   $76.00   $76.00   $76.00  
  Purchase #7 $5.66   13.387%   $6.4177   $6.42   $6.40   $6.40  
  7 purchase totals = $661.78       $714.9156   $714.93   $714.90   $714.90