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 $214.33   11.791%   $239.6017   $239.60   $239.60   $239.60  
  Purchase #2 $57.62   8.775%   $62.6762   $62.68   $62.70   $62.70  
  Purchase #3 $135.45   6.849%   $144.727   $144.73   $144.75   $144.70  
  Purchase #4 $192.87   5.151%   $202.8047   $202.80   $202.80   $202.80  
  Purchase #5 $119.61   13.459%   $135.7083   $135.71   $135.70   $135.70  
  Purchase #6 $51.32   5.814%   $54.3037   $54.30   $54.30   $54.30  
  Purchase #7 $173.54   8.508%   $188.3048   $188.30   $188.30   $188.30  
  7 purchase totals = $944.74       $1,028.1264   $1,028.12   $1,028.15   $1,028.10