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 $240.36   8.573%   $260.9661   $260.97   $260.95   $261.00  
  Purchase #2 $207.88   10.440%   $229.5827   $229.58   $229.60   $229.60  
  Purchase #3 $250.42   6.723%   $267.2557   $267.26   $267.25   $267.30  
  Purchase #4 $20.65   12.184%   $23.166   $23.17   $23.15   $23.20  
  Purchase #5 $119.92   6.323%   $127.5025   $127.50   $127.50   $127.50  
  Purchase #6 $161.25   13.586%   $183.1574   $183.16   $183.15   $183.20  
  Purchase #7 $39.79   6.786%   $42.4901   $42.49   $42.50   $42.50  
  7 purchase totals = $1,040.27       $1,134.1205   $1,134.13   $1,134.10   $1,134.30