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 $104.84   9.646%   $114.9529   $114.95   $114.95   $115.00  
  Purchase #2 $16.89   8.460%   $18.3189   $18.32   $18.30   $18.30  
  Purchase #3 $166.69   5.533%   $175.913   $175.91   $175.90   $175.90  
  Purchase #4 $186.43   6.736%   $198.9879   $198.99   $199.00   $199.00  
  Purchase #5 $250.42   4.576%   $261.8792   $261.88   $261.90   $261.90  
  Purchase #6 $167.97   7.800%   $181.0717   $181.07   $181.05   $181.10  
  Purchase #7 $74.43   6.806%   $79.4957   $79.50   $79.50   $79.50  
  7 purchase totals = $967.67       $1,030.6193   $1,030.62   $1,030.60   $1,030.70