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 $39.43   13.179%   $44.6265   $44.63   $44.65   $44.60  
  Purchase #2 $107.63   11.341%   $119.8363   $119.84   $119.85   $119.80  
  Purchase #3 $105.87   8.343%   $114.7027   $114.70   $114.70   $114.70  
  Purchase #4 $222.83   6.275%   $236.8126   $236.81   $236.80   $236.80  
  Purchase #5 $98.44   4.343%   $102.7152   $102.72   $102.70   $102.70  
  Purchase #6 $61.36   3.628%   $63.5861   $63.59   $63.60   $63.60  
  Purchase #7 $249.91   5.765%   $264.3173   $264.32   $264.30   $264.30  
  7 purchase totals = $885.47       $946.5967   $946.61   $946.60   $946.50