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 $24.29   8.448%   $26.342   $26.34   $26.35   $26.30  
  Purchase #2 $147.95   11.358%   $164.7542   $164.75   $164.75   $164.80  
  Purchase #3 $244.86   7.827%   $264.0252   $264.03   $264.05   $264.00  
  Purchase #4 $59.67   7.768%   $64.3052   $64.31   $64.30   $64.30  
  Purchase #5 $53.62   4.321%   $55.9369   $55.94   $55.95   $55.90  
  Purchase #6 $161.27   8.514%   $175.0005   $175.00   $175.00   $175.00  
  Purchase #7 $206.66   7.509%   $222.1781   $222.18   $222.20   $222.20  
  7 purchase totals = $898.32       $972.5421   $972.55   $972.60   $972.50