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 $234.72   8.651%   $255.0256   $255.03   $255.05   $255.00  
  Purchase #2 $227.77   11.524%   $254.0182   $254.02   $254.00   $254.00  
  Purchase #3 $41.73   13.599%   $47.4049   $47.40   $47.40   $47.40  
  Purchase #4 $146.72   8.552%   $159.2675   $159.27   $159.25   $159.30  
  Purchase #5 $149.65   13.857%   $170.387   $170.39   $170.40   $170.40  
  Purchase #6 $83.38   9.194%   $91.046   $91.05   $91.05   $91.00  
  Purchase #7 $42.49   8.280%   $46.0082   $46.01   $46.00   $46.00  
  7 purchase totals = $926.46       $1,023.1574   $1,023.17   $1,023.15   $1,023.10