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 $22.63   13.783%   $25.7491   $25.75   $25.75   $25.70  
  Purchase #2 $49.25   8.190%   $53.2836   $53.28   $53.30   $53.30  
  Purchase #3 $14.27   9.469%   $15.6212   $15.62   $15.60   $15.60  
  Purchase #4 $44.36   12.667%   $49.9791   $49.98   $50.00   $50.00  
  Purchase #5 $69.73   11.296%   $77.6067   $77.61   $77.60   $77.60  
  Purchase #6 $152.94   6.853%   $163.421   $163.42   $163.40   $163.40  
  Purchase #7 $104.72   8.256%   $113.3657   $113.37   $113.35   $113.40  
  7 purchase totals = $457.90       $499.0264   $499.03   $499.00   $499.00