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 $93.26   5.277%   $98.1813   $98.18   $98.20   $98.20  
  Purchase #2 $87.78   9.811%   $96.3921   $96.39   $96.40   $96.40  
  Purchase #3 $63.42   4.374%   $66.194   $66.19   $66.20   $66.20  
  Purchase #4 $234.88   6.416%   $249.9499   $249.95   $249.95   $249.90  
  Purchase #5 $234.63   9.614%   $257.1873   $257.19   $257.20   $257.20  
  Purchase #6 $93.53   10.725%   $103.5611   $103.56   $103.55   $103.60  
  Purchase #7 $108.93   5.727%   $115.1684   $115.17   $115.15   $115.20  
  7 purchase totals = $916.43       $986.6341   $986.63   $986.65   $986.70