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 $96.42   8.491%   $104.607   $104.61   $104.60   $104.60  
  Purchase #2 $213.31   11.406%   $237.6401   $237.64   $237.65   $237.60  
  Purchase #3 $186.87   11.666%   $208.6703   $208.67   $208.65   $208.70  
  Purchase #4 $66.70   8.478%   $72.3548   $72.35   $72.35   $72.40  
  Purchase #5 $52.85   3.335%   $54.6125   $54.61   $54.60   $54.60  
  Purchase #6 $219.34   7.838%   $236.5319   $236.53   $236.55   $236.50  
  Purchase #7 $155.69   12.177%   $174.6484   $174.65   $174.65   $174.60  
  7 purchase totals = $991.18       $1,089.0650   $1,089.06   $1,089.05   $1,089.00