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 $77.27   6.316%   $82.1504   $82.15   $82.15   $82.20  
  Purchase #2 $233.42   12.221%   $261.9463   $261.95   $261.95   $261.90  
  Purchase #3 $247.50   13.714%   $281.4422   $281.44   $281.45   $281.40  
  Purchase #4 $144.62   5.847%   $153.0759   $153.08   $153.10   $153.10  
  Purchase #5 $191.53   13.629%   $217.6336   $217.63   $217.65   $217.60  
  Purchase #6 $236.88   9.642%   $259.72   $259.72   $259.70   $259.70  
  Purchase #7 $28.44   6.557%   $30.3048   $30.30   $30.30   $30.30  
  7 purchase totals = $1,159.66       $1,286.2732   $1,286.27   $1,286.30   $1,286.20