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 $248.70   7.486%   $267.3177   $267.32   $267.30   $267.30  
  Purchase #2 $143.40   8.508%   $155.6005   $155.60   $155.60   $155.60  
  Purchase #3 $105.60   8.529%   $114.6066   $114.61   $114.60   $114.60  
  Purchase #4 $53.99   11.486%   $60.1913   $60.19   $60.20   $60.20  
  Purchase #5 $118.79   9.635%   $130.2354   $130.24   $130.25   $130.20  
  Purchase #6 $237.86   4.522%   $248.616   $248.62   $248.60   $248.60  
  Purchase #7 $235.84   12.218%   $264.6549   $264.65   $264.65   $264.70  
  7 purchase totals = $1,144.18       $1,241.2224   $1,241.23   $1,241.20   $1,241.20