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 $58.47   13.479%   $66.3512   $66.35   $66.35   $66.40  
  Purchase #2 $241.92   8.378%   $262.1881   $262.19   $262.20   $262.20  
  Purchase #3 $214.46   13.269%   $242.9167   $242.92   $242.90   $242.90  
  Purchase #4 $89.66   9.720%   $98.375   $98.38   $98.40   $98.40  
  Purchase #5 $73.47   10.532%   $81.2079   $81.21   $81.20   $81.20  
  Purchase #6 $217.77   6.572%   $232.0818   $232.08   $232.10   $232.10  
  Purchase #7 $35.68   12.366%   $40.0922   $40.09   $40.10   $40.10  
  7 purchase totals = $931.43       $1,023.2129   $1,023.22   $1,023.25   $1,023.30