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 $24.41   9.639%   $26.7629   $26.76   $26.75   $26.80  
  Purchase #2 $46.75   4.601%   $48.901   $48.90   $48.90   $48.90  
  Purchase #3 $183.33   7.616%   $197.2924   $197.29   $197.30   $197.30  
  Purchase #4 $30.31   4.580%   $31.6982   $31.70   $31.70   $31.70  
  Purchase #5 $152.62   9.602%   $167.2746   $167.27   $167.25   $167.30  
  Purchase #6 $220.43   5.755%   $233.1157   $233.12   $233.10   $233.10  
  Purchase #7 $233.81   6.179%   $248.2571   $248.26   $248.25   $248.30  
  7 purchase totals = $891.66       $953.3019   $953.30   $953.25   $953.40