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 $30.82   5.833%   $32.6177   $32.62   $32.60   $32.60  
  Purchase #2 $67.81   3.436%   $70.14   $70.14   $70.15   $70.10  
  Purchase #3 $48.96   6.517%   $52.1507   $52.15   $52.15   $52.20  
  Purchase #4 $109.96   6.773%   $117.4076   $117.41   $117.40   $117.40  
  Purchase #5 $241.40   8.748%   $262.5177   $262.52   $262.50   $262.50  
  Purchase #6 $62.82   11.249%   $69.8866   $69.89   $69.90   $69.90  
  Purchase #7 $73.97   4.817%   $77.5331   $77.53   $77.55   $77.50  
  7 purchase totals = $635.74       $682.2534   $682.26   $682.25   $682.20