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 $190.83   10.533%   $210.9301   $210.93   $210.95   $210.90  
  Purchase #2 $212.25   6.803%   $226.6894   $226.69   $226.70   $226.70  
  Purchase #3 $85.78   8.723%   $93.2626   $93.26   $93.25   $93.30  
  Purchase #4 $152.80   5.553%   $161.285   $161.29   $161.30   $161.30  
  Purchase #5 $106.60   7.326%   $114.4095   $114.41   $114.40   $114.40  
  Purchase #6 $47.88   11.150%   $53.2186   $53.22   $53.20   $53.20  
  Purchase #7 $176.29   8.854%   $191.8987   $191.90   $191.90   $191.90  
  7 purchase totals = $972.43       $1,051.6939   $1,051.70   $1,051.70   $1,051.70