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 $36.47   13.689%   $41.4624   $41.46   $41.45   $41.50  
  Purchase #2 $66.67   10.869%   $73.9164   $73.92   $73.90   $73.90  
  Purchase #3 $55.44   5.304%   $58.3805   $58.38   $58.40   $58.40  
  Purchase #4 $191.45   5.450%   $201.884   $201.88   $201.90   $201.90  
  Purchase #5 $241.73   13.324%   $273.9381   $273.94   $273.95   $273.90  
  Purchase #6 $65.93   13.678%   $74.9479   $74.95   $74.95   $74.90  
  Purchase #7 $73.75   8.804%   $80.243   $80.24   $80.25   $80.20  
  7 purchase totals = $731.44       $804.7723   $804.77   $804.80   $804.70