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 $54.25   12.227%   $60.8831   $60.88   $60.90   $60.90  
  Purchase #2 $248.86   3.605%   $257.8314   $257.83   $257.85   $257.80  
  Purchase #3 $219.45   6.497%   $233.7077   $233.71   $233.70   $233.70  
  Purchase #4 $238.37   9.844%   $261.8351   $261.84   $261.85   $261.80  
  Purchase #5 $41.66   3.730%   $43.2139   $43.21   $43.20   $43.20  
  Purchase #6 $104.29   9.212%   $113.8972   $113.90   $113.90   $113.90  
  Purchase #7 $227.44   8.112%   $245.8899   $245.89   $245.90   $245.90  
  7 purchase totals = $1,134.32       $1,217.2583   $1,217.26   $1,217.30   $1,217.20