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 $43.79   10.473%   $48.3761   $48.38   $48.40   $48.40  
  Purchase #2 $226.89   7.333%   $243.5278   $243.53   $243.55   $243.50  
  Purchase #3 $249.99   6.826%   $267.0543   $267.05   $267.05   $267.10  
  Purchase #4 $171.49   6.565%   $182.7483   $182.75   $182.75   $182.70  
  Purchase #5 $180.31   5.546%   $190.31   $190.31   $190.30   $190.30  
  Purchase #6 $140.96   12.385%   $158.4179   $158.42   $158.40   $158.40  
  Purchase #7 $103.48   13.628%   $117.5823   $117.58   $117.60   $117.60  
  7 purchase totals = $1,116.91       $1,208.0167   $1,208.02   $1,208.05   $1,208.00