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 $125.84   10.664%   $139.2596   $139.26   $139.25   $139.30  
  Purchase #2 $202.62   11.482%   $225.8848   $225.88   $225.90   $225.90  
  Purchase #3 $8.29   11.437%   $9.2381   $9.24   $9.25   $9.20  
  Purchase #4 $226.95   9.540%   $248.601   $248.60   $248.60   $248.60  
  Purchase #5 $212.61   11.418%   $236.8858   $236.89   $236.90   $236.90  
  Purchase #6 $233.69   3.615%   $242.1379   $242.14   $242.15   $242.10  
  Purchase #7 $55.95   12.455%   $62.9186   $62.92   $62.90   $62.90  
  7 purchase totals = $1,065.95       $1,164.9258   $1,164.93   $1,164.95   $1,164.90