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 $63.58   8.391%   $68.915   $68.92   $68.90   $68.90  
  Purchase #2 $44.68   9.212%   $48.7959   $48.80   $48.80   $48.80  
  Purchase #3 $134.34   6.273%   $142.7671   $142.77   $142.75   $142.80  
  Purchase #4 $93.72   13.298%   $106.1829   $106.18   $106.20   $106.20  
  Purchase #5 $189.45   13.167%   $214.3949   $214.39   $214.40   $214.40  
  Purchase #6 $104.91   8.840%   $114.184   $114.18   $114.20   $114.20  
  Purchase #7 $173.63   8.618%   $188.5934   $188.59   $188.60   $188.60  
  7 purchase totals = $804.31       $883.8332   $883.83   $883.85   $883.90