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 $234.53   11.661%   $261.8785   $261.88   $261.90   $261.90  
  Purchase #2 $129.93   7.408%   $139.5552   $139.56   $139.55   $139.60  
  Purchase #3 $100.32   10.576%   $110.9298   $110.93   $110.95   $110.90  
  Purchase #4 $173.64   10.150%   $191.2645   $191.26   $191.25   $191.30  
  Purchase #5 $17.76   10.747%   $19.6687   $19.67   $19.65   $19.70  
  Purchase #6 $15.61   11.708%   $17.4376   $17.44   $17.45   $17.40  
  Purchase #7 $22.27   4.446%   $23.2601   $23.26   $23.25   $23.30  
  7 purchase totals = $694.06       $763.9944   $764.00   $764.00   $764.10