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 $55.87   10.481%   $61.7257   $61.73   $61.75   $61.70  
  Purchase #2 $46.38   6.448%   $49.3706   $49.37   $49.35   $49.40  
  Purchase #3 $47.27   7.838%   $50.975   $50.98   $51.00   $51.00  
  Purchase #4 $211.61   7.350%   $227.1633   $227.16   $227.15   $227.20  
  Purchase #5 $76.34   7.254%   $81.8777   $81.88   $81.90   $81.90  
  Purchase #6 $177.95   13.366%   $201.7348   $201.73   $201.75   $201.70  
  Purchase #7 $136.96   3.221%   $141.3715   $141.37   $141.35   $141.40  
  7 purchase totals = $752.38       $814.2186   $814.22   $814.25   $814.30