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 $83.41   10.213%   $91.9287   $91.93   $91.95   $91.90  
  Purchase #2 $214.60   8.430%   $232.6908   $232.69   $232.70   $232.70  
  Purchase #3 $157.28   12.514%   $176.962   $176.96   $176.95   $177.00  
  Purchase #4 $64.87   7.160%   $69.5147   $69.51   $69.50   $69.50  
  Purchase #5 $214.63   4.741%   $224.8056   $224.81   $224.80   $224.80  
  Purchase #6 $87.80   12.703%   $98.9532   $98.95   $98.95   $99.00  
  Purchase #7 $90.99   13.868%   $103.6085   $103.61   $103.60   $103.60  
  7 purchase totals = $913.58       $998.4635   $998.46   $998.45   $998.50