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 $246.70   6.169%   $261.9189   $261.92   $261.90   $261.90  
  Purchase #2 $96.78   7.289%   $103.8343   $103.83   $103.85   $103.80  
  Purchase #3 $21.90   11.704%   $24.4632   $24.46   $24.45   $24.50  
  Purchase #4 $25.41   13.347%   $28.8015   $28.80   $28.80   $28.80  
  Purchase #5 $31.86   9.697%   $34.9495   $34.95   $34.95   $34.90  
  Purchase #6 $180.27   9.328%   $197.0856   $197.09   $197.10   $197.10  
  Purchase #7 $213.47   13.202%   $241.6523   $241.65   $241.65   $241.70  
  7 purchase totals = $816.39       $892.7053   $892.70   $892.70   $892.70