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 $214.37   13.448%   $243.1985   $243.20   $243.20   $243.20  
  Purchase #2 $227.62   10.226%   $250.8964   $250.90   $250.90   $250.90  
  Purchase #3 $142.56   10.578%   $157.64   $157.64   $157.65   $157.60  
  Purchase #4 $24.87   5.165%   $26.1545   $26.15   $26.15   $26.20  
  Purchase #5 $68.57   6.306%   $72.894   $72.89   $72.90   $72.90  
  Purchase #6 $9.31   10.247%   $10.264   $10.26   $10.25   $10.30  
  Purchase #7 $152.71   10.614%   $168.9186   $168.92   $168.90   $168.90  
  7 purchase totals = $840.01       $929.9660   $929.96   $929.95   $930.00