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 $228.84   13.416%   $259.5412   $259.54   $259.55   $259.50  
  Purchase #2 $61.40   5.253%   $64.6253   $64.63   $64.65   $64.60  
  Purchase #3 $95.76   9.738%   $105.0851   $105.09   $105.10   $105.10  
  Purchase #4 $226.70   11.291%   $252.2967   $252.30   $252.30   $252.30  
  Purchase #5 $76.48   3.122%   $78.8677   $78.87   $78.85   $78.90  
  Purchase #6 $195.96   9.544%   $214.6624   $214.66   $214.65   $214.70  
  Purchase #7 $54.62   13.815%   $62.1658   $62.17   $62.15   $62.20  
  7 purchase totals = $939.76       $1,037.2442   $1,037.26   $1,037.25   $1,037.30