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 $21.81   7.347%   $23.4124   $23.41   $23.40   $23.40  
  Purchase #2 $84.89   12.204%   $95.25   $95.25   $95.25   $95.30  
  Purchase #3 $59.79   13.194%   $67.6787   $67.68   $67.70   $67.70  
  Purchase #4 $227.61   8.751%   $247.5282   $247.53   $247.55   $247.50  
  Purchase #5 $127.79   9.633%   $140.1   $140.10   $140.10   $140.10  
  Purchase #6 $107.34   6.830%   $114.6713   $114.67   $114.65   $114.70  
  Purchase #7 $71.39   4.640%   $74.7025   $74.70   $74.70   $74.70  
  7 purchase totals = $700.62       $763.3431   $763.34   $763.35   $763.40