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 $208.79   10.302%   $230.2995   $230.30   $230.30   $230.30  
  Purchase #2 $241.53   10.306%   $266.4221   $266.42   $266.40   $266.40  
  Purchase #3 $249.86   4.815%   $261.8908   $261.89   $261.90   $261.90  
  Purchase #4 $61.39   7.133%   $65.7689   $65.77   $65.75   $65.80  
  Purchase #5 $197.55   6.698%   $210.7819   $210.78   $210.80   $210.80  
  Purchase #6 $76.89   6.102%   $81.5818   $81.58   $81.60   $81.60  
  Purchase #7 $167.59   13.652%   $190.4694   $190.47   $190.45   $190.50  
  7 purchase totals = $1,203.60       $1,307.2144   $1,307.21   $1,307.20   $1,307.30