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 $250.83   4.472%   $262.0471   $262.05   $262.05   $262.00  
  Purchase #2 $79.75   8.459%   $86.4961   $86.50   $86.50   $86.50  
  Purchase #3 $136.29   5.374%   $143.6142   $143.61   $143.60   $143.60  
  Purchase #4 $107.87   8.525%   $117.0659   $117.07   $117.05   $117.10  
  Purchase #5 $244.73   13.334%   $277.3623   $277.36   $277.35   $277.40  
  Purchase #6 $144.81   13.347%   $164.1378   $164.14   $164.15   $164.10  
  Purchase #7 $111.51   12.258%   $125.1789   $125.18   $125.20   $125.20  
  7 purchase totals = $1,075.79       $1,175.9023   $1,175.91   $1,175.90   $1,175.90