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 $171.73   8.164%   $185.75   $185.75   $185.75   $185.80  
  Purchase #2 $229.92   13.828%   $261.7133   $261.71   $261.70   $261.70  
  Purchase #3 $65.39   8.614%   $71.0227   $71.02   $71.00   $71.00  
  Purchase #4 $120.65   13.230%   $136.612   $136.61   $136.60   $136.60  
  Purchase #5 $170.59   7.418%   $183.2444   $183.24   $183.25   $183.20  
  Purchase #6 $27.99   8.122%   $30.2633   $30.26   $30.25   $30.30  
  Purchase #7 $126.50   10.388%   $139.6408   $139.64   $139.65   $139.60  
  7 purchase totals = $912.77       $1,008.2465   $1,008.23   $1,008.20   $1,008.20