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 $114.38   4.142%   $119.1176   $119.12   $119.10   $119.10  
  Purchase #2 $60.36   10.782%   $66.868   $66.87   $66.85   $66.90  
  Purchase #3 $231.26   9.538%   $253.3176   $253.32   $253.30   $253.30  
  Purchase #4 $214.81   3.659%   $222.6699   $222.67   $222.65   $222.70  
  Purchase #5 $213.89   11.852%   $239.2402   $239.24   $239.25   $239.20  
  Purchase #6 $201.30   13.862%   $229.2042   $229.20   $229.20   $229.20  
  Purchase #7 $182.31   6.447%   $194.0635   $194.06   $194.05   $194.10  
  7 purchase totals = $1,218.31       $1,324.4810   $1,324.48   $1,324.40   $1,324.50