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 $83.94   13.426%   $95.2098   $95.21   $95.20   $95.20  
  Purchase #2 $237.92   9.270%   $259.9752   $259.98   $260.00   $260.00  
  Purchase #3 $249.27   4.777%   $261.1776   $261.18   $261.20   $261.20  
  Purchase #4 $175.88   8.376%   $190.6117   $190.61   $190.60   $190.60  
  Purchase #5 $56.69   5.512%   $59.8148   $59.81   $59.80   $59.80  
  Purchase #6 $23.27   9.704%   $25.5281   $25.53   $25.55   $25.50  
  Purchase #7 $25.44   9.690%   $27.9051   $27.91   $27.90   $27.90  
  7 purchase totals = $852.41       $920.2223   $920.23   $920.25   $920.20