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 $228.95   13.376%   $259.5744   $259.57   $259.55   $259.60  
  Purchase #2 $175.87   11.731%   $196.5013   $196.50   $196.50   $196.50  
  Purchase #3 $56.67   9.669%   $62.1494   $62.15   $62.15   $62.10  
  Purchase #4 $198.94   4.410%   $207.7133   $207.71   $207.70   $207.70  
  Purchase #5 $43.31   7.845%   $46.7077   $46.71   $46.70   $46.70  
  Purchase #6 $15.34   11.187%   $17.0561   $17.06   $17.05   $17.10  
  Purchase #7 $14.96   11.872%   $16.7361   $16.74   $16.75   $16.70  
  7 purchase totals = $734.04       $806.4383   $806.44   $806.40   $806.40