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 $93.41   5.552%   $98.5961   $98.60   $98.60   $98.60  
  Purchase #2 $127.35   6.301%   $135.3743   $135.37   $135.35   $135.40  
  Purchase #3 $228.76   5.555%   $241.4676   $241.47   $241.45   $241.50  
  Purchase #4 $44.53   4.828%   $46.6799   $46.68   $46.70   $46.70  
  Purchase #5 $229.79   8.213%   $248.6627   $248.66   $248.65   $248.70  
  Purchase #6 $111.40   10.250%   $122.8185   $122.82   $122.80   $122.80  
  Purchase #7 $116.91   11.371%   $130.2038   $130.20   $130.20   $130.20  
  7 purchase totals = $952.15       $1,023.8029   $1,023.80   $1,023.75   $1,023.90