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 $47.56   4.518%   $49.7088   $49.71   $49.70   $49.70  
  Purchase #2 $62.76   13.499%   $71.232   $71.23   $71.25   $71.20  
  Purchase #3 $58.66   9.629%   $64.3084   $64.31   $64.30   $64.30  
  Purchase #4 $114.60   13.834%   $130.4538   $130.45   $130.45   $130.50  
  Purchase #5 $24.53   6.427%   $26.1065   $26.11   $26.10   $26.10  
  Purchase #6 $121.41   4.240%   $126.5578   $126.56   $126.55   $126.60  
  Purchase #7 $228.77   11.553%   $255.1998   $255.20   $255.20   $255.20  
  7 purchase totals = $658.29       $723.5671   $723.57   $723.55   $723.60