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 $86.81   13.687%   $98.6917   $98.69   $98.70   $98.70  
  Purchase #2 $109.62   5.371%   $115.5077   $115.51   $115.50   $115.50  
  Purchase #3 $42.33   13.127%   $47.8867   $47.89   $47.90   $47.90  
  Purchase #4 $237.94   3.168%   $245.4779   $245.48   $245.50   $245.50  
  Purchase #5 $150.47   12.633%   $169.4789   $169.48   $169.50   $169.50  
  Purchase #6 $154.39   12.166%   $173.1731   $173.17   $173.15   $173.20  
  Purchase #7 $204.49   10.705%   $226.3807   $226.38   $226.40   $226.40  
  7 purchase totals = $986.05       $1,076.5967   $1,076.60   $1,076.65   $1,076.70