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 $195.44   6.481%   $208.1065   $208.11   $208.10   $208.10  
  Purchase #2 $216.38   9.305%   $236.5142   $236.51   $236.50   $236.50  
  Purchase #3 $246.30   13.391%   $279.282   $279.28   $279.30   $279.30  
  Purchase #4 $65.75   8.274%   $71.1902   $71.19   $71.20   $71.20  
  Purchase #5 $89.45   6.810%   $95.5415   $95.54   $95.55   $95.50  
  Purchase #6 $125.78   7.242%   $134.889   $134.89   $134.90   $134.90  
  Purchase #7 $220.64   9.777%   $242.212   $242.21   $242.20   $242.20  
  7 purchase totals = $1,159.74       $1,267.7354   $1,267.73   $1,267.75   $1,267.70