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 $24.59   5.694%   $25.9902   $25.99   $26.00   $26.00  
  Purchase #2 $15.40   7.218%   $16.5116   $16.51   $16.50   $16.50  
  Purchase #3 $135.76   11.680%   $151.6168   $151.62   $151.60   $151.60  
  Purchase #4 $8.55   4.260%   $8.9142   $8.91   $8.90   $8.90  
  Purchase #5 $90.81   11.794%   $101.5201   $101.52   $101.50   $101.50  
  Purchase #6 $206.83   9.600%   $226.6857   $226.69   $226.70   $226.70  
  Purchase #7 $220.65   4.212%   $229.9438   $229.94   $229.95   $229.90  
  7 purchase totals = $702.59       $761.1824   $761.18   $761.15   $761.10