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 $175.63   6.381%   $186.837   $186.84   $186.85   $186.80  
  Purchase #2 $232.84   7.242%   $249.7023   $249.70   $249.70   $249.70  
  Purchase #3 $53.39   12.719%   $60.1807   $60.18   $60.20   $60.20  
  Purchase #4 $196.59   5.684%   $207.7642   $207.76   $207.75   $207.80  
  Purchase #5 $69.94   6.209%   $74.2826   $74.28   $74.30   $74.30  
  Purchase #6 $244.48   3.412%   $252.8217   $252.82   $252.80   $252.80  
  Purchase #7 $122.30   12.357%   $137.4126   $137.41   $137.40   $137.40  
  7 purchase totals = $1,095.17       $1,169.0011   $1,168.99   $1,169.00   $1,169.00