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 $190.86   11.631%   $213.0589   $213.06   $213.05   $213.10  
  Purchase #2 $79.41   8.577%   $86.221   $86.22   $86.20   $86.20  
  Purchase #3 $46.92   11.630%   $52.3768   $52.38   $52.40   $52.40  
  Purchase #4 $52.92   3.514%   $54.7796   $54.78   $54.80   $54.80  
  Purchase #5 $235.98   13.827%   $268.609   $268.61   $268.60   $268.60  
  Purchase #6 $22.49   3.566%   $23.292   $23.29   $23.30   $23.30  
  Purchase #7 $235.87   9.215%   $257.6054   $257.61   $257.60   $257.60  
  7 purchase totals = $864.45       $955.9427   $955.95   $955.95   $956.00