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 $8.60   3.471%   $8.8985   $8.90   $8.90   $8.90  
  Purchase #2 $35.91   11.753%   $40.1305   $40.13   $40.15   $40.10  
  Purchase #3 $39.57   7.296%   $42.457   $42.46   $42.45   $42.50  
  Purchase #4 $114.62   13.171%   $129.7166   $129.72   $129.70   $129.70  
  Purchase #5 $139.32   13.205%   $157.7172   $157.72   $157.70   $157.70  
  Purchase #6 $20.63   9.274%   $22.5432   $22.54   $22.55   $22.50  
  Purchase #7 $57.49   8.105%   $62.1496   $62.15   $62.15   $62.10  
  7 purchase totals = $416.14       $463.6126   $463.62   $463.60   $463.50