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 $240.48   10.332%   $265.3264   $265.33   $265.35   $265.30  
  Purchase #2 $249.41   4.733%   $261.2146   $261.21   $261.20   $261.20  
  Purchase #3 $173.58   11.167%   $192.9637   $192.96   $192.95   $193.00  
  Purchase #4 $250.39   8.153%   $270.8043   $270.80   $270.80   $270.80  
  Purchase #5 $196.88   4.688%   $206.1097   $206.11   $206.10   $206.10  
  Purchase #6 $5.31   11.830%   $5.9382   $5.94   $5.95   $5.90  
  Purchase #7 $28.66   5.442%   $30.2197   $30.22   $30.20   $30.20  
  7 purchase totals = $1,144.71       $1,232.5766   $1,232.57   $1,232.55   $1,232.50