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 $23.44   10.674%   $25.942   $25.94   $25.95   $25.90  
  Purchase #2 $189.59   12.750%   $213.7627   $213.76   $213.75   $213.80  
  Purchase #3 $35.76   8.394%   $38.7617   $38.76   $38.75   $38.80  
  Purchase #4 $67.74   9.290%   $74.033   $74.03   $74.05   $74.00  
  Purchase #5 $128.41   12.856%   $144.9184   $144.92   $144.90   $144.90  
  Purchase #6 $48.38   3.419%   $50.0341   $50.03   $50.05   $50.00  
  Purchase #7 $44.71   11.788%   $49.9804   $49.98   $50.00   $50.00  
  7 purchase totals = $538.03       $597.4323   $597.42   $597.45   $597.40