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 $152.74   10.613%   $168.9503   $168.95   $168.95   $169.00  
  Purchase #2 $123.45   10.360%   $136.2394   $136.24   $136.25   $136.20  
  Purchase #3 $61.89   12.363%   $69.5415   $69.54   $69.55   $69.50  
  Purchase #4 $155.27   10.710%   $171.8994   $171.90   $171.90   $171.90  
  Purchase #5 $109.90   11.193%   $122.2011   $122.20   $122.20   $122.20  
  Purchase #6 $224.74   13.298%   $254.6259   $254.63   $254.65   $254.60  
  Purchase #7 $70.57   5.670%   $74.5713   $74.57   $74.55   $74.60  
  7 purchase totals = $898.56       $998.0289   $998.03   $998.05   $998.00