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 $68.61   13.212%   $77.6748   $77.67   $77.65   $77.70  
  Purchase #2 $28.36   5.803%   $30.0057   $30.01   $30.00   $30.00  
  Purchase #3 $229.61   8.212%   $248.4656   $248.47   $248.45   $248.50  
  Purchase #4 $61.81   6.809%   $66.0186   $66.02   $66.00   $66.00  
  Purchase #5 $243.66   7.239%   $261.2985   $261.30   $261.30   $261.30  
  Purchase #6 $245.25   5.158%   $257.9   $257.90   $257.90   $257.90  
  Purchase #7 $51.93   5.706%   $54.8931   $54.89   $54.90   $54.90  
  7 purchase totals = $929.23       $996.2563   $996.26   $996.20   $996.30