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 $61.42   3.254%   $63.4186   $63.42   $63.40   $63.40  
  Purchase #2 $55.68   10.275%   $61.4011   $61.40   $61.40   $61.40  
  Purchase #3 $201.47   11.471%   $224.5806   $224.58   $224.60   $224.60  
  Purchase #4 $30.88   11.246%   $34.3528   $34.35   $34.35   $34.40  
  Purchase #5 $114.80   13.637%   $130.4553   $130.46   $130.45   $130.50  
  Purchase #6 $130.25   4.853%   $136.571   $136.57   $136.55   $136.60  
  Purchase #7 $181.92   3.181%   $187.7069   $187.71   $187.70   $187.70  
  7 purchase totals = $776.42       $838.4863   $838.49   $838.45   $838.60