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 $211.27   12.158%   $236.9562   $236.96   $236.95   $237.00  
  Purchase #2 $60.77   5.158%   $63.9045   $63.90   $63.90   $63.90  
  Purchase #3 $72.62   11.595%   $81.0403   $81.04   $81.05   $81.00  
  Purchase #4 $22.76   11.819%   $25.45   $25.45   $25.45   $25.50  
  Purchase #5 $228.97   12.271%   $257.0669   $257.07   $257.05   $257.10  
  Purchase #6 $22.27   7.339%   $23.9044   $23.90   $23.90   $23.90  
  Purchase #7 $22.93   11.509%   $25.569   $25.57   $25.55   $25.60  
  7 purchase totals = $641.59       $713.8913   $713.89   $713.85   $714.00