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 $248.84   7.211%   $266.7839   $266.78   $266.80   $266.80  
  Purchase #2 $133.39   3.338%   $137.8426   $137.84   $137.85   $137.80  
  Purchase #3 $23.52   13.604%   $26.7197   $26.72   $26.70   $26.70  
  Purchase #4 $242.36   3.258%   $250.2561   $250.26   $250.25   $250.30  
  Purchase #5 $84.92   4.345%   $88.6098   $88.61   $88.60   $88.60  
  Purchase #6 $68.62   9.424%   $75.0867   $75.09   $75.10   $75.10  
  Purchase #7 $14.83   5.122%   $15.5896   $15.59   $15.60   $15.60  
  7 purchase totals = $816.48       $860.8884   $860.89   $860.90   $860.90