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 $105.75   13.124%   $119.6286   $119.63   $119.65   $119.60  
  Purchase #2 $125.60   6.392%   $133.6284   $133.63   $133.65   $133.60  
  Purchase #3 $224.51   6.662%   $239.4669   $239.47   $239.45   $239.50  
  Purchase #4 $104.80   8.308%   $113.5068   $113.51   $113.50   $113.50  
  Purchase #5 $180.39   13.655%   $205.0223   $205.02   $205.00   $205.00  
  Purchase #6 $117.91   5.164%   $123.9989   $124.00   $124.00   $124.00  
  Purchase #7 $212.38   7.319%   $227.9241   $227.92   $227.90   $227.90  
  7 purchase totals = $1,071.34       $1,163.1760   $1,163.18   $1,163.15   $1,163.10