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 $54.95   5.524%   $57.9854   $57.99   $58.00   $58.00  
  Purchase #2 $46.51   12.288%   $52.2251   $52.23   $52.25   $52.20  
  Purchase #3 $116.31   9.410%   $127.2548   $127.25   $127.25   $127.30  
  Purchase #4 $166.40   13.465%   $188.8058   $188.81   $188.80   $188.80  
  Purchase #5 $242.42   6.102%   $257.2125   $257.21   $257.20   $257.20  
  Purchase #6 $155.80   4.725%   $163.1616   $163.16   $163.15   $163.20  
  Purchase #7 $98.74   9.269%   $107.8922   $107.89   $107.90   $107.90  
  7 purchase totals = $881.13       $954.5374   $954.54   $954.55   $954.60