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 $24.88   6.343%   $26.4581   $26.46   $26.45   $26.50  
  Purchase #2 $58.86   3.630%   $60.9966   $61.00   $61.00   $61.00  
  Purchase #3 $105.70   7.546%   $113.6761   $113.68   $113.70   $113.70  
  Purchase #4 $71.97   3.662%   $74.6055   $74.61   $74.60   $74.60  
  Purchase #5 $11.35   3.414%   $11.7375   $11.74   $11.75   $11.70  
  Purchase #6 $86.77   10.117%   $95.5485   $95.55   $95.55   $95.50  
  Purchase #7 $116.89   4.823%   $122.5276   $122.53   $122.55   $122.50  
  7 purchase totals = $476.42       $505.5499   $505.57   $505.60   $505.50