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 $186.60   6.493%   $198.7159   $198.72   $198.70   $198.70  
  Purchase #2 $110.45   8.271%   $119.5853   $119.59   $119.60   $119.60  
  Purchase #3 $63.63   7.836%   $68.616   $68.62   $68.60   $68.60  
  Purchase #4 $200.91   8.806%   $218.6021   $218.60   $218.60   $218.60  
  Purchase #5 $128.79   12.139%   $144.4238   $144.42   $144.40   $144.40  
  Purchase #6 $107.27   6.479%   $114.22   $114.22   $114.20   $114.20  
  Purchase #7 $99.59   3.295%   $102.8715   $102.87   $102.85   $102.90  
  7 purchase totals = $897.24       $967.0346   $967.04   $966.95   $967.00