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 $57.94   13.223%   $65.6014   $65.60   $65.60   $65.60  
  Purchase #2 $59.39   4.687%   $62.1736   $62.17   $62.15   $62.20  
  Purchase #3 $104.44   6.367%   $111.0897   $111.09   $111.10   $111.10  
  Purchase #4 $35.84   12.326%   $40.2576   $40.26   $40.25   $40.30  
  Purchase #5 $217.59   3.425%   $225.0425   $225.04   $225.05   $225.00  
  Purchase #6 $228.49   3.813%   $237.2023   $237.20   $237.20   $237.20  
  Purchase #7 $198.58   9.635%   $217.7132   $217.71   $217.70   $217.70  
  7 purchase totals = $902.27       $959.0803   $959.07   $959.05   $959.10