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 $173.48   13.302%   $196.5563   $196.56   $196.55   $196.60  
  Purchase #2 $132.30   4.463%   $138.2045   $138.20   $138.20   $138.20  
  Purchase #3 $68.43   5.534%   $72.2169   $72.22   $72.20   $72.20  
  Purchase #4 $58.87   9.548%   $64.4909   $64.49   $64.50   $64.50  
  Purchase #5 $11.55   9.271%   $12.6208   $12.62   $12.60   $12.60  
  Purchase #6 $154.36   13.217%   $174.7618   $174.76   $174.75   $174.80  
  Purchase #7 $54.29   5.471%   $57.2602   $57.26   $57.25   $57.30  
  7 purchase totals = $653.28       $716.1114   $716.11   $716.05   $716.20