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 $240.49   8.758%   $261.5521   $261.55   $261.55   $261.60  
  Purchase #2 $174.50   11.742%   $194.9898   $194.99   $195.00   $195.00  
  Purchase #3 $104.34   8.119%   $112.8114   $112.81   $112.80   $112.80  
  Purchase #4 $90.76   5.732%   $95.9624   $95.96   $95.95   $96.00  
  Purchase #5 $123.89   12.259%   $139.0777   $139.08   $139.10   $139.10  
  Purchase #6 $107.44   13.695%   $122.1539   $122.15   $122.15   $122.20  
  Purchase #7 $155.61   10.637%   $172.1622   $172.16   $172.15   $172.20  
  7 purchase totals = $997.03       $1,098.7095   $1,098.70   $1,098.70   $1,098.90