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 $61.75   4.464%   $64.5065   $64.51   $64.50   $64.50  
  Purchase #2 $232.69   3.772%   $241.4671   $241.47   $241.45   $241.50  
  Purchase #3 $76.42   4.436%   $79.81   $79.81   $79.80   $79.80  
  Purchase #4 $224.96   5.104%   $236.442   $236.44   $236.45   $236.40  
  Purchase #5 $225.58   11.108%   $250.6374   $250.64   $250.65   $250.60  
  Purchase #6 $70.38   9.125%   $76.8022   $76.80   $76.80   $76.80  
  Purchase #7 $144.67   6.321%   $153.8146   $153.81   $153.80   $153.80  
  7 purchase totals = $1,036.45       $1,103.4798   $1,103.48   $1,103.45   $1,103.40