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 $87.50   10.426%   $96.6228   $96.62   $96.60   $96.60  
  Purchase #2 $75.50   4.147%   $78.631   $78.63   $78.65   $78.60  
  Purchase #3 $12.75   8.763%   $13.8673   $13.87   $13.85   $13.90  
  Purchase #4 $241.83   8.213%   $261.6915   $261.69   $261.70   $261.70  
  Purchase #5 $136.55   13.293%   $154.7016   $154.70   $154.70   $154.70  
  Purchase #6 $174.70   13.395%   $198.1011   $198.10   $198.10   $198.10  
  Purchase #7 $131.96   12.439%   $148.3745   $148.37   $148.35   $148.40  
  7 purchase totals = $860.79       $951.9898   $951.98   $951.95   $952.00