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 $55.34   13.417%   $62.765   $62.77   $62.75   $62.80  
  Purchase #2 $24.98   4.287%   $26.0509   $26.05   $26.05   $26.10  
  Purchase #3 $85.96   11.714%   $96.0294   $96.03   $96.05   $96.00  
  Purchase #4 $249.48   4.176%   $259.8983   $259.90   $259.90   $259.90  
  Purchase #5 $180.80   5.476%   $190.7006   $190.70   $190.70   $190.70  
  Purchase #6 $144.49   8.257%   $156.4205   $156.42   $156.40   $156.40  
  Purchase #7 $16.92   12.223%   $18.9881   $18.99   $19.00   $19.00  
  7 purchase totals = $757.97       $810.8528   $810.86   $810.85   $810.90