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 $215.78   8.271%   $233.6272   $233.63   $233.65   $233.60  
  Purchase #2 $113.61   12.351%   $127.642   $127.64   $127.65   $127.60  
  Purchase #3 $27.32   9.587%   $29.9392   $29.94   $29.95   $29.90  
  Purchase #4 $104.94   4.327%   $109.4808   $109.48   $109.50   $109.50  
  Purchase #5 $69.62   7.120%   $74.5769   $74.58   $74.60   $74.60  
  Purchase #6 $162.61   6.688%   $173.4854   $173.49   $173.50   $173.50  
  Purchase #7 $7.97   13.839%   $9.073   $9.07   $9.05   $9.10  
  7 purchase totals = $701.85       $757.8245   $757.83   $757.90   $757.80