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 $52.84   11.723%   $59.0344   $59.03   $59.05   $59.00  
  Purchase #2 $50.26   10.467%   $55.5207   $55.52   $55.50   $55.50  
  Purchase #3 $52.52   9.421%   $57.4679   $57.47   $57.45   $57.50  
  Purchase #4 $157.28   3.608%   $162.9547   $162.95   $162.95   $163.00  
  Purchase #5 $221.38   5.558%   $233.6843   $233.68   $233.70   $233.70  
  Purchase #6 $83.28   11.353%   $92.7348   $92.73   $92.75   $92.70  
  Purchase #7 $248.81   13.609%   $282.6706   $282.67   $282.65   $282.70  
  7 purchase totals = $866.37       $944.0674   $944.05   $944.05   $944.10