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 $227.71   5.506%   $240.2477   $240.25   $240.25   $240.20  
  Purchase #2 $104.58   12.322%   $117.4663   $117.47   $117.45   $117.50  
  Purchase #3 $106.26   5.647%   $112.2605   $112.26   $112.25   $112.30  
  Purchase #4 $57.64   4.733%   $60.3681   $60.37   $60.35   $60.40  
  Purchase #5 $49.99   9.540%   $54.759   $54.76   $54.75   $54.80  
  Purchase #6 $201.34   8.581%   $218.617   $218.62   $218.60   $218.60  
  Purchase #7 $196.69   4.541%   $205.6217   $205.62   $205.60   $205.60  
  7 purchase totals = $944.21       $1,009.3403   $1,009.35   $1,009.25   $1,009.40