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 $227.39   6.360%   $241.852   $241.85   $241.85   $241.90  
  Purchase #2 $28.40   8.671%   $30.8626   $30.86   $30.85   $30.90  
  Purchase #3 $245.81   6.371%   $261.4706   $261.47   $261.45   $261.50  
  Purchase #4 $228.64   5.765%   $241.8211   $241.82   $241.80   $241.80  
  Purchase #5 $160.49   7.504%   $172.5332   $172.53   $172.55   $172.50  
  Purchase #6 $189.27   6.718%   $201.9852   $201.99   $202.00   $202.00  
  Purchase #7 $102.82   11.587%   $114.7338   $114.73   $114.75   $114.70  
  7 purchase totals = $1,182.82       $1,265.2585   $1,265.25   $1,265.25   $1,265.30