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 $10.26   12.208%   $11.5125   $11.51   $11.50   $11.50  
  Purchase #2 $73.65   3.271%   $76.0591   $76.06   $76.05   $76.10  
  Purchase #3 $246.38   9.536%   $269.8748   $269.87   $269.85   $269.90  
  Purchase #4 $62.72   4.800%   $65.7306   $65.73   $65.75   $65.70  
  Purchase #5 $65.70   7.662%   $70.7339   $70.73   $70.75   $70.70  
  Purchase #6 $209.29   10.850%   $231.998   $232.00   $232.00   $232.00  
  Purchase #7 $31.30   13.663%   $35.5765   $35.58   $35.60   $35.60  
  7 purchase totals = $699.30       $761.4854   $761.48   $761.50   $761.50