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 $61.36   12.742%   $69.1785   $69.18   $69.20   $69.20  
  Purchase #2 $160.90   6.853%   $171.9265   $171.93   $171.95   $171.90  
  Purchase #3 $161.75   13.628%   $183.7933   $183.79   $183.80   $183.80  
  Purchase #4 $15.93   11.848%   $17.8174   $17.82   $17.80   $17.80  
  Purchase #5 $72.54   4.813%   $76.0314   $76.03   $76.05   $76.00  
  Purchase #6 $46.29   6.718%   $49.3998   $49.40   $49.40   $49.40  
  Purchase #7 $86.95   3.545%   $90.0324   $90.03   $90.05   $90.00  
  7 purchase totals = $605.72       $658.1793   $658.18   $658.25   $658.10