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 $162.89   10.674%   $180.2769   $180.28   $180.30   $180.30  
  Purchase #2 $60.51   7.591%   $65.1033   $65.10   $65.10   $65.10  
  Purchase #3 $115.70   9.246%   $126.3976   $126.40   $126.40   $126.40  
  Purchase #4 $124.31   4.302%   $129.6578   $129.66   $129.65   $129.70  
  Purchase #5 $15.51   13.350%   $17.5806   $17.58   $17.60   $17.60  
  Purchase #6 $28.99   6.360%   $30.8338   $30.83   $30.85   $30.80  
  Purchase #7 $249.49   4.814%   $261.5004   $261.50   $261.50   $261.50  
  7 purchase totals = $757.40       $811.3504   $811.35   $811.40   $811.40