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 $77.69   11.463%   $86.5956   $86.60   $86.60   $86.60  
  Purchase #2 $244.51   5.211%   $257.2514   $257.25   $257.25   $257.30  
  Purchase #3 $50.89   13.257%   $57.6365   $57.64   $57.65   $57.60  
  Purchase #4 $77.80   6.725%   $83.0321   $83.03   $83.05   $83.00  
  Purchase #5 $44.29   4.623%   $46.3375   $46.34   $46.35   $46.30  
  Purchase #6 $56.93   11.463%   $63.4559   $63.46   $63.45   $63.50  
  Purchase #7 $168.41   8.536%   $182.7855   $182.79   $182.80   $182.80  
  7 purchase totals = $720.52       $777.0945   $777.11   $777.15   $777.10