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 $183.92   6.328%   $195.5585   $195.56   $195.55   $195.60  
  Purchase #2 $179.63   11.849%   $200.9144   $200.91   $200.90   $200.90  
  Purchase #3 $92.37   6.285%   $98.1755   $98.18   $98.20   $98.20  
  Purchase #4 $115.65   12.475%   $130.0773   $130.08   $130.10   $130.10  
  Purchase #5 $238.29   9.732%   $261.4804   $261.48   $261.50   $261.50  
  Purchase #6 $246.50   5.172%   $259.249   $259.25   $259.25   $259.20  
  Purchase #7 $200.57   10.757%   $222.1453   $222.15   $222.15   $222.10  
  7 purchase totals = $1,256.93       $1,367.6004   $1,367.61   $1,367.65   $1,367.60