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 $235.66   7.466%   $253.2544   $253.25   $253.25   $253.30  
  Purchase #2 $190.90   12.705%   $215.1538   $215.15   $215.15   $215.20  
  Purchase #3 $114.49   6.223%   $121.6147   $121.61   $121.60   $121.60  
  Purchase #4 $242.65   8.172%   $262.4794   $262.48   $262.50   $262.50  
  Purchase #5 $203.45   13.774%   $231.4732   $231.47   $231.45   $231.50  
  Purchase #6 $11.76   5.249%   $12.3773   $12.38   $12.40   $12.40  
  Purchase #7 $150.76   9.280%   $164.7505   $164.75   $164.75   $164.80  
  7 purchase totals = $1,149.67       $1,261.1033   $1,261.09   $1,261.10   $1,261.30