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 $23.63   6.538%   $25.1749   $25.17   $25.15   $25.20  
  Purchase #2 $146.59   8.292%   $158.7452   $158.75   $158.75   $158.70  
  Purchase #3 $218.71   13.606%   $248.4677   $248.47   $248.45   $248.50  
  Purchase #4 $208.95   7.629%   $224.8908   $224.89   $224.90   $224.90  
  Purchase #5 $84.55   10.435%   $93.3728   $93.37   $93.35   $93.40  
  Purchase #6 $125.36   7.776%   $135.108   $135.11   $135.10   $135.10  
  Purchase #7 $63.97   7.391%   $68.698   $68.70   $68.70   $68.70  
  7 purchase totals = $871.76       $954.4574   $954.46   $954.40   $954.50