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 $34.61   13.349%   $39.2301   $39.23   $39.25   $39.20  
  Purchase #2 $224.54   5.848%   $237.6711   $237.67   $237.65   $237.70  
  Purchase #3 $244.98   9.585%   $268.4613   $268.46   $268.45   $268.50  
  Purchase #4 $76.27   6.545%   $81.2619   $81.26   $81.25   $81.30  
  Purchase #5 $170.84   13.847%   $194.4962   $194.50   $194.50   $194.50  
  Purchase #6 $47.81   5.519%   $50.4486   $50.45   $50.45   $50.40  
  Purchase #7 $23.57   5.526%   $24.8725   $24.87   $24.85   $24.90  
  7 purchase totals = $822.62       $896.4417   $896.44   $896.40   $896.50