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 $40.58   7.184%   $43.4953   $43.50   $43.50   $43.50  
  Purchase #2 $198.33   5.840%   $209.9125   $209.91   $209.90   $209.90  
  Purchase #3 $245.71   5.636%   $259.5582   $259.56   $259.55   $259.60  
  Purchase #4 $236.46   10.746%   $261.87   $261.87   $261.85   $261.90  
  Purchase #5 $127.48   5.644%   $134.675   $134.68   $134.70   $134.70  
  Purchase #6 $165.35   12.458%   $185.9493   $185.95   $185.95   $185.90  
  Purchase #7 $204.44   5.741%   $216.1769   $216.18   $216.20   $216.20  
  7 purchase totals = $1,218.35       $1,311.6372   $1,311.65   $1,311.65   $1,311.70