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 $23.53   4.239%   $24.5274   $24.53   $24.55   $24.50  
  Purchase #2 $116.55   8.801%   $126.8076   $126.81   $126.80   $126.80  
  Purchase #3 $86.56   13.253%   $98.0318   $98.03   $98.05   $98.00  
  Purchase #4 $186.79   4.807%   $195.769   $195.77   $195.75   $195.80  
  Purchase #5 $34.79   13.584%   $39.5159   $39.52   $39.50   $39.50  
  Purchase #6 $156.76   12.480%   $176.3236   $176.32   $176.30   $176.30  
  Purchase #7 $56.96   12.298%   $63.9649   $63.96   $63.95   $64.00  
  7 purchase totals = $661.94       $724.9402   $724.94   $724.90   $724.90