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 $244.53   7.397%   $262.6179   $262.62   $262.60   $262.60  
  Purchase #2 $178.98   5.529%   $188.8758   $188.88   $188.90   $188.90  
  Purchase #3 $183.81   4.195%   $191.5208   $191.52   $191.50   $191.50  
  Purchase #4 $43.79   8.141%   $47.3549   $47.35   $47.35   $47.40  
  Purchase #5 $57.57   13.641%   $65.4231   $65.42   $65.40   $65.40  
  Purchase #6 $238.40   5.274%   $250.9732   $250.97   $250.95   $251.00  
  Purchase #7 $248.88   5.202%   $261.8267   $261.83   $261.85   $261.80  
  7 purchase totals = $1,195.96       $1,268.5924   $1,268.59   $1,268.55   $1,268.60