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 $248.80   10.420%   $274.725   $274.73   $274.75   $274.70  
  Purchase #2 $245.88   6.328%   $261.4393   $261.44   $261.45   $261.40  
  Purchase #3 $76.29   7.293%   $81.8538   $81.85   $81.85   $81.90  
  Purchase #4 $161.45   10.715%   $178.7494   $178.75   $178.75   $178.70  
  Purchase #5 $174.49   8.445%   $189.2257   $189.23   $189.25   $189.20  
  Purchase #6 $163.88   5.336%   $172.6246   $172.62   $172.60   $172.60  
  Purchase #7 $215.46   9.402%   $235.7175   $235.72   $235.70   $235.70  
  7 purchase totals = $1,286.25       $1,394.3353   $1,394.34   $1,394.35   $1,394.20