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 $60.29   9.476%   $66.0031   $66.00   $66.00   $66.00  
  Purchase #2 $54.25   12.528%   $61.0464   $61.05   $61.05   $61.00  
  Purchase #3 $102.81   6.283%   $109.2696   $109.27   $109.25   $109.30  
  Purchase #4 $56.49   8.726%   $61.4193   $61.42   $61.40   $61.40  
  Purchase #5 $111.47   11.735%   $124.551   $124.55   $124.55   $124.60  
  Purchase #6 $37.37   10.685%   $41.363   $41.36   $41.35   $41.40  
  Purchase #7 $21.63   4.681%   $22.6425   $22.64   $22.65   $22.60  
  7 purchase totals = $444.31       $486.2949   $486.29   $486.25   $486.30