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 $64.99   5.573%   $68.6119   $68.61   $68.60   $68.60  
  Purchase #2 $112.71   8.806%   $122.6352   $122.64   $122.65   $122.60  
  Purchase #3 $111.47   13.545%   $126.5686   $126.57   $126.55   $126.60  
  Purchase #4 $157.63   8.113%   $170.4185   $170.42   $170.40   $170.40  
  Purchase #5 $187.44   5.567%   $197.8748   $197.87   $197.85   $197.90  
  Purchase #6 $123.78   8.626%   $134.4573   $134.46   $134.45   $134.50  
  Purchase #7 $60.28   3.111%   $62.1553   $62.16   $62.15   $62.20  
  7 purchase totals = $818.30       $882.7216   $882.73   $882.65   $882.80