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 $114.47   8.487%   $124.1851   $124.19   $124.20   $124.20  
  Purchase #2 $88.37   10.560%   $97.7019   $97.70   $97.70   $97.70  
  Purchase #3 $90.66   11.676%   $101.2455   $101.25   $101.25   $101.20  
  Purchase #4 $185.44   8.783%   $201.7272   $201.73   $201.75   $201.70  
  Purchase #5 $146.48   5.719%   $154.8572   $154.86   $154.85   $154.90  
  Purchase #6 $74.60   13.566%   $84.7202   $84.72   $84.70   $84.70  
  Purchase #7 $73.91   6.734%   $78.8871   $78.89   $78.90   $78.90  
  7 purchase totals = $773.93       $843.3242   $843.34   $843.35   $843.30