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 $42.84   11.455%   $47.7473   $47.75   $47.75   $47.70  
  Purchase #2 $26.84   3.114%   $27.6758   $27.68   $27.70   $27.70  
  Purchase #3 $233.32   11.868%   $261.0104   $261.01   $261.00   $261.00  
  Purchase #4 $33.82   7.164%   $36.2429   $36.24   $36.25   $36.20  
  Purchase #5 $51.39   4.553%   $53.7298   $53.73   $53.75   $53.70  
  Purchase #6 $63.83   8.124%   $69.0155   $69.02   $69.00   $69.00  
  Purchase #7 $119.35   6.210%   $126.7616   $126.76   $126.75   $126.80  
  7 purchase totals = $571.39       $622.1833   $622.19   $622.20   $622.10