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 $48.88   8.553%   $53.0607   $53.06   $53.05   $53.10  
  Purchase #2 $140.36   10.182%   $154.6515   $154.65   $154.65   $154.70  
  Purchase #3 $82.27   5.131%   $86.4913   $86.49   $86.50   $86.50  
  Purchase #4 $224.72   4.349%   $234.4931   $234.49   $234.50   $234.50  
  Purchase #5 $92.91   5.151%   $97.6958   $97.70   $97.70   $97.70  
  Purchase #6 $14.67   5.247%   $15.4397   $15.44   $15.45   $15.40  
  Purchase #7 $142.83   9.712%   $156.7016   $156.70   $156.70   $156.70  
  7 purchase totals = $746.64       $798.5337   $798.53   $798.55   $798.60