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 $205.64   5.157%   $216.2449   $216.24   $216.25   $216.20  
  Purchase #2 $43.48   9.547%   $47.631   $47.63   $47.65   $47.60  
  Purchase #3 $246.93   11.129%   $274.4108   $274.41   $274.40   $274.40  
  Purchase #4 $239.88   9.510%   $262.6926   $262.69   $262.70   $262.70  
  Purchase #5 $193.76   12.547%   $218.0711   $218.07   $218.05   $218.10  
  Purchase #6 $215.83   4.571%   $225.6956   $225.70   $225.70   $225.70  
  Purchase #7 $249.91   11.315%   $278.1873   $278.19   $278.20   $278.20  
  7 purchase totals = $1,395.43       $1,522.9333   $1,522.93   $1,522.95   $1,522.90