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 $24.66   9.842%   $27.087   $27.09   $27.10   $27.10  
  Purchase #2 $176.69   9.634%   $193.7123   $193.71   $193.70   $193.70  
  Purchase #3 $47.71   4.809%   $50.0044   $50.00   $50.00   $50.00  
  Purchase #4 $211.95   4.358%   $221.1868   $221.19   $221.20   $221.20  
  Purchase #5 $34.38   8.416%   $37.2734   $37.27   $37.25   $37.30  
  Purchase #6 $44.80   4.794%   $46.9477   $46.95   $46.95   $46.90  
  Purchase #7 $247.89   12.502%   $278.8812   $278.88   $278.90   $278.90  
  7 purchase totals = $788.08       $855.0928   $855.09   $855.10   $855.10