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 $82.96   12.670%   $93.471   $93.47   $93.45   $93.50  
  Purchase #2 $114.32   8.708%   $124.275   $124.28   $124.30   $124.30  
  Purchase #3 $121.91   10.789%   $135.0629   $135.06   $135.05   $135.10  
  Purchase #4 $99.36   8.233%   $107.5403   $107.54   $107.55   $107.50  
  Purchase #5 $245.45   5.114%   $258.0023   $258.00   $258.00   $258.00  
  Purchase #6 $42.84   8.224%   $46.3632   $46.36   $46.35   $46.40  
  Purchase #7 $28.28   8.766%   $30.759   $30.76   $30.75   $30.80  
  7 purchase totals = $735.12       $795.4737   $795.47   $795.45   $795.60