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 $112.44   6.426%   $119.6654   $119.67   $119.65   $119.70  
  Purchase #2 $111.42   6.571%   $118.7414   $118.74   $118.75   $118.70  
  Purchase #3 $201.84   12.338%   $226.743   $226.74   $226.75   $226.70  
  Purchase #4 $160.59   13.662%   $182.5298   $182.53   $182.55   $182.50  
  Purchase #5 $136.25   9.798%   $149.5998   $149.60   $149.60   $149.60  
  Purchase #6 $227.46   5.428%   $239.8065   $239.81   $239.80   $239.80  
  Purchase #7 $43.99   11.584%   $49.0858   $49.09   $49.10   $49.10  
  7 purchase totals = $993.99       $1,086.1717   $1,086.18   $1,086.20   $1,086.10