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 $59.67   5.159%   $62.7484   $62.75   $62.75   $62.70  
  Purchase #2 $23.89   11.781%   $26.7045   $26.70   $26.70   $26.70  
  Purchase #3 $125.55   4.677%   $131.422   $131.42   $131.40   $131.40  
  Purchase #4 $177.57   3.587%   $183.9394   $183.94   $183.95   $183.90  
  Purchase #5 $23.53   8.265%   $25.4748   $25.47   $25.45   $25.50  
  Purchase #6 $127.80   9.355%   $139.7557   $139.76   $139.75   $139.80  
  Purchase #7 $74.99   7.488%   $80.6053   $80.61   $80.60   $80.60  
  7 purchase totals = $613.00       $650.6501   $650.65   $650.60   $650.60