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 $179.56   8.415%   $194.67   $194.67   $194.65   $194.70  
  Purchase #2 $9.38   3.712%   $9.7282   $9.73   $9.75   $9.70  
  Purchase #3 $56.90   5.437%   $59.9937   $59.99   $60.00   $60.00  
  Purchase #4 $71.86   9.311%   $78.5509   $78.55   $78.55   $78.60  
  Purchase #5 $157.25   4.271%   $163.9661   $163.97   $163.95   $164.00  
  Purchase #6 $239.97   9.468%   $262.6904   $262.69   $262.70   $262.70  
  Purchase #7 $31.50   12.108%   $35.314   $35.31   $35.30   $35.30  
  7 purchase totals = $746.42       $804.9133   $804.91   $804.90   $805.00