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 $165.70   10.744%   $183.5028   $183.50   $183.50   $183.50  
  Purchase #2 $50.31   11.696%   $56.1943   $56.19   $56.20   $56.20  
  Purchase #3 $240.38   11.804%   $268.7545   $268.75   $268.75   $268.80  
  Purchase #4 $41.46   11.838%   $46.368   $46.37   $46.35   $46.40  
  Purchase #5 $77.50   8.522%   $84.1046   $84.10   $84.10   $84.10  
  Purchase #6 $103.59   10.172%   $114.1272   $114.13   $114.15   $114.10  
  Purchase #7 $173.75   11.120%   $193.071   $193.07   $193.05   $193.10  
  7 purchase totals = $852.69       $946.1224   $946.11   $946.10   $946.20