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 $248.58   8.491%   $269.6869   $269.69   $269.70   $269.70  
  Purchase #2 $250.58   3.141%   $258.4507   $258.45   $258.45   $258.50  
  Purchase #3 $7.44   12.691%   $8.3842   $8.38   $8.40   $8.40  
  Purchase #4 $30.45   11.350%   $33.9061   $33.91   $33.90   $33.90  
  Purchase #5 $205.67   11.116%   $228.5323   $228.53   $228.55   $228.50  
  Purchase #6 $196.95   13.509%   $223.556   $223.56   $223.55   $223.60  
  Purchase #7 $90.99   12.216%   $102.1053   $102.11   $102.10   $102.10  
  7 purchase totals = $1,030.66       $1,124.6215   $1,124.63   $1,124.65   $1,124.70