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 $58.78   8.152%   $63.5717   $63.57   $63.55   $63.60  
  Purchase #2 $83.84   10.363%   $92.5283   $92.53   $92.55   $92.50  
  Purchase #3 $248.37   10.342%   $274.0564   $274.06   $274.05   $274.10  
  Purchase #4 $30.47   7.783%   $32.8415   $32.84   $32.85   $32.80  
  Purchase #5 $169.90   5.169%   $178.6821   $178.68   $178.70   $178.70  
  Purchase #6 $54.97   4.594%   $57.4953   $57.50   $57.50   $57.50  
  Purchase #7 $236.64   10.611%   $261.7499   $261.75   $261.75   $261.70  
  7 purchase totals = $882.97       $960.9252   $960.93   $960.95   $960.90