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 $190.71   8.280%   $206.5008   $206.50   $206.50   $206.50  
  Purchase #2 $156.55   3.252%   $161.641   $161.64   $161.65   $161.60  
  Purchase #3 $35.72   6.296%   $37.9689   $37.97   $37.95   $38.00  
  Purchase #4 $69.39   7.389%   $74.5172   $74.52   $74.50   $74.50  
  Purchase #5 $115.40   13.541%   $131.0263   $131.03   $131.05   $131.00  
  Purchase #6 $149.29   12.677%   $168.2155   $168.22   $168.20   $168.20  
  Purchase #7 $242.76   4.587%   $253.8954   $253.90   $253.90   $253.90  
  7 purchase totals = $959.82       $1,033.7651   $1,033.78   $1,033.75   $1,033.70