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 $76.92   13.802%   $87.5365   $87.54   $87.55   $87.50  
  Purchase #2 $94.44   10.544%   $104.3978   $104.40   $104.40   $104.40  
  Purchase #3 $157.26   13.724%   $178.8424   $178.84   $178.85   $178.80  
  Purchase #4 $240.37   8.872%   $261.6956   $261.70   $261.70   $261.70  
  Purchase #5 $239.89   5.114%   $252.158   $252.16   $252.15   $252.20  
  Purchase #6 $217.25   8.215%   $235.0971   $235.10   $235.10   $235.10  
  Purchase #7 $240.42   8.624%   $261.1538   $261.15   $261.15   $261.20  
  7 purchase totals = $1,266.55       $1,380.8812   $1,380.89   $1,380.90   $1,380.90