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 $51.57   13.694%   $58.632   $58.63   $58.65   $58.60  
  Purchase #2 $105.36   3.633%   $109.1877   $109.19   $109.20   $109.20  
  Purchase #3 $24.46   3.587%   $25.3374   $25.34   $25.35   $25.30  
  Purchase #4 $73.70   5.657%   $77.8692   $77.87   $77.85   $77.90  
  Purchase #5 $206.36   3.756%   $214.1109   $214.11   $214.10   $214.10  
  Purchase #6 $197.91   5.502%   $208.799   $208.80   $208.80   $208.80  
  Purchase #7 $199.38   4.451%   $208.2544   $208.25   $208.25   $208.30  
  7 purchase totals = $858.74       $902.1906   $902.19   $902.20   $902.20