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 $238.31   3.202%   $245.9407   $245.94   $245.95   $245.90  
  Purchase #2 $51.84   13.766%   $58.9763   $58.98   $59.00   $59.00  
  Purchase #3 $48.76   11.724%   $54.4766   $54.48   $54.50   $54.50  
  Purchase #4 $223.67   5.376%   $235.6945   $235.69   $235.70   $235.70  
  Purchase #5 $114.44   3.300%   $118.2165   $118.22   $118.20   $118.20  
  Purchase #6 $57.66   10.524%   $63.7281   $63.73   $63.75   $63.70  
  Purchase #7 $59.73   11.531%   $66.6175   $66.62   $66.60   $66.60  
  7 purchase totals = $794.41       $843.6502   $843.66   $843.70   $843.60