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 $214.95   5.669%   $227.1355   $227.14   $227.15   $227.10  
  Purchase #2 $145.50   12.851%   $164.1982   $164.20   $164.20   $164.20  
  Purchase #3 $63.34   7.665%   $68.195   $68.20   $68.20   $68.20  
  Purchase #4 $115.83   8.263%   $125.401   $125.40   $125.40   $125.40  
  Purchase #5 $35.67   6.309%   $37.9204   $37.92   $37.90   $37.90  
  Purchase #6 $127.80   12.706%   $144.0383   $144.04   $144.05   $144.00  
  Purchase #7 $223.81   5.664%   $236.4866   $236.49   $236.50   $236.50  
  7 purchase totals = $926.90       $1,003.3750   $1,003.39   $1,003.40   $1,003.30