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 $113.65   11.277%   $126.4663   $126.47   $126.45   $126.50  
  Purchase #2 $59.69   3.106%   $61.544   $61.54   $61.55   $61.50  
  Purchase #3 $218.36   8.503%   $236.9272   $236.93   $236.95   $236.90  
  Purchase #4 $154.70   12.850%   $174.579   $174.58   $174.60   $174.60  
  Purchase #5 $156.41   9.371%   $171.0672   $171.07   $171.05   $171.10  
  Purchase #6 $230.47   12.860%   $260.1084   $260.11   $260.10   $260.10  
  Purchase #7 $195.63   9.155%   $213.5399   $213.54   $213.55   $213.50  
  7 purchase totals = $1,128.91       $1,244.2320   $1,244.24   $1,244.25   $1,244.20