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 $65.92   11.777%   $73.6834   $73.68   $73.70   $73.70  
  Purchase #2 $49.84   3.762%   $51.715   $51.72   $51.70   $51.70  
  Purchase #3 $61.28   11.105%   $68.0851   $68.09   $68.10   $68.10  
  Purchase #4 $75.43   11.770%   $84.3081   $84.31   $84.30   $84.30  
  Purchase #5 $104.41   8.652%   $113.4436   $113.44   $113.45   $113.40  
  Purchase #6 $197.91   4.788%   $207.3859   $207.39   $207.40   $207.40  
  Purchase #7 $178.64   4.388%   $186.4787   $186.48   $186.50   $186.50  
  7 purchase totals = $733.43       $785.0998   $785.11   $785.15   $785.10