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 $189.95   10.167%   $209.2622   $209.26   $209.25   $209.30  
  Purchase #2 $118.91   3.347%   $122.8899   $122.89   $122.90   $122.90  
  Purchase #3 $132.90   6.617%   $141.694   $141.69   $141.70   $141.70  
  Purchase #4 $36.68   4.133%   $38.196   $38.20   $38.20   $38.20  
  Purchase #5 $138.86   3.528%   $143.759   $143.76   $143.75   $143.80  
  Purchase #6 $137.69   11.562%   $153.6097   $153.61   $153.60   $153.60  
  Purchase #7 $222.41   5.276%   $234.1444   $234.14   $234.15   $234.10  
  7 purchase totals = $977.40       $1,043.5552   $1,043.55   $1,043.55   $1,043.60