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 $231.25   13.294%   $261.9924   $261.99   $262.00   $262.00  
  Purchase #2 $14.31   3.300%   $14.7822   $14.78   $14.80   $14.80  
  Purchase #3 $172.77   7.462%   $185.6621   $185.66   $185.65   $185.70  
  Purchase #4 $177.95   13.351%   $201.7081   $201.71   $201.70   $201.70  
  Purchase #5 $48.97   7.187%   $52.4895   $52.49   $52.50   $52.50  
  Purchase #6 $76.48   13.123%   $86.5165   $86.52   $86.50   $86.50  
  Purchase #7 $50.83   11.647%   $56.7502   $56.75   $56.75   $56.80  
  7 purchase totals = $772.56       $859.9010   $859.90   $859.90   $860.00