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 $60.26   11.834%   $67.3912   $67.39   $67.40   $67.40  
  Purchase #2 $215.68   11.605%   $240.7097   $240.71   $240.70   $240.70  
  Purchase #3 $105.26   8.332%   $114.0303   $114.03   $114.05   $114.00  
  Purchase #4 $142.54   11.114%   $158.3819   $158.38   $158.40   $158.40  
  Purchase #5 $153.88   13.762%   $175.057   $175.06   $175.05   $175.10  
  Purchase #6 $27.62   5.874%   $29.2424   $29.24   $29.25   $29.20  
  Purchase #7 $185.87   8.262%   $201.2266   $201.23   $201.25   $201.20  
  7 purchase totals = $891.11       $986.0391   $986.04   $986.10   $986.00