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 $174.57   13.518%   $198.1684   $198.17   $198.15   $198.20  
  Purchase #2 $135.38   12.218%   $151.9207   $151.92   $151.90   $151.90  
  Purchase #3 $20.54   13.296%   $23.271   $23.27   $23.25   $23.30  
  Purchase #4 $105.85   8.121%   $114.4461   $114.45   $114.45   $114.40  
  Purchase #5 $210.49   13.289%   $238.462   $238.46   $238.45   $238.50  
  Purchase #6 $207.46   3.577%   $214.8808   $214.88   $214.90   $214.90  
  Purchase #7 $9.32   3.208%   $9.619   $9.62   $9.60   $9.60  
  7 purchase totals = $863.61       $950.7680   $950.77   $950.70   $950.80