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 $183.69   5.201%   $193.2437   $193.24   $193.25   $193.20  
  Purchase #2 $135.44   4.617%   $141.6933   $141.69   $141.70   $141.70  
  Purchase #3 $101.88   8.842%   $110.8882   $110.89   $110.90   $110.90  
  Purchase #4 $78.84   12.533%   $88.721   $88.72   $88.70   $88.70  
  Purchase #5 $95.31   7.248%   $102.2181   $102.22   $102.20   $102.20  
  Purchase #6 $207.34   12.132%   $232.4945   $232.49   $232.50   $232.50  
  Purchase #7 $136.27   13.770%   $155.0344   $155.03   $155.05   $155.00  
  7 purchase totals = $938.77       $1,024.2932   $1,024.28   $1,024.30   $1,024.20