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 $154.93   13.648%   $176.0748   $176.07   $176.05   $176.10  
  Purchase #2 $244.91   4.565%   $256.0901   $256.09   $256.10   $256.10  
  Purchase #3 $51.30   6.172%   $54.4662   $54.47   $54.45   $54.50  
  Purchase #4 $249.64   3.774%   $259.0614   $259.06   $259.05   $259.10  
  Purchase #5 $113.75   6.719%   $121.3929   $121.39   $121.40   $121.40  
  Purchase #6 $209.50   13.463%   $237.705   $237.71   $237.70   $237.70  
  Purchase #7 $143.96   12.247%   $161.5908   $161.59   $161.60   $161.60  
  7 purchase totals = $1,167.99       $1,266.3812   $1,266.38   $1,266.35   $1,266.50