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 $205.35   4.293%   $214.1657   $214.17   $214.15   $214.20  
  Purchase #2 $239.63   5.866%   $253.6867   $253.69   $253.70   $253.70  
  Purchase #3 $55.39   8.277%   $59.9746   $59.97   $59.95   $60.00  
  Purchase #4 $227.59   9.797%   $249.887   $249.89   $249.90   $249.90  
  Purchase #5 $121.53   8.383%   $131.7179   $131.72   $131.70   $131.70  
  Purchase #6 $206.88   13.614%   $235.0446   $235.04   $235.05   $235.00  
  Purchase #7 $122.53   3.161%   $126.4032   $126.40   $126.40   $126.40  
  7 purchase totals = $1,178.90       $1,270.8797   $1,270.88   $1,270.85   $1,270.90