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 $214.69   12.730%   $242.02   $242.02   $242.00   $242.00  
  Purchase #2 $197.84   7.773%   $213.2181   $213.22   $213.20   $213.20  
  Purchase #3 $81.69   5.312%   $86.0294   $86.03   $86.05   $86.00  
  Purchase #4 $183.51   11.849%   $205.2541   $205.25   $205.25   $205.30  
  Purchase #5 $133.86   7.181%   $143.4725   $143.47   $143.45   $143.50  
  Purchase #6 $214.81   7.448%   $230.809   $230.81   $230.80   $230.80  
  Purchase #7 $126.90   10.317%   $139.9923   $139.99   $140.00   $140.00  
  7 purchase totals = $1,153.30       $1,260.7954   $1,260.79   $1,260.75   $1,260.80