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 $64.44   13.531%   $73.1594   $73.16   $73.15   $73.20  
  Purchase #2 $52.87   5.349%   $55.698   $55.70   $55.70   $55.70  
  Purchase #3 $15.90   10.209%   $17.5232   $17.52   $17.50   $17.50  
  Purchase #4 $135.62   3.413%   $140.2487   $140.25   $140.25   $140.20  
  Purchase #5 $222.64   11.734%   $248.7646   $248.76   $248.75   $248.80  
  Purchase #6 $209.96   8.444%   $227.689   $227.69   $227.70   $227.70  
  Purchase #7 $250.82   13.512%   $284.7108   $284.71   $284.70   $284.70  
  7 purchase totals = $952.25       $1,047.7937   $1,047.79   $1,047.75   $1,047.80