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 $164.61   13.563%   $186.9361   $186.94   $186.95   $186.90  
  Purchase #2 $47.35   13.763%   $53.8668   $53.87   $53.85   $53.90  
  Purchase #3 $109.55   5.791%   $115.894   $115.89   $115.90   $115.90  
  Purchase #4 $208.93   12.218%   $234.4571   $234.46   $234.45   $234.50  
  Purchase #5 $139.50   10.621%   $154.3163   $154.32   $154.30   $154.30  
  Purchase #6 $153.99   11.159%   $171.1737   $171.17   $171.15   $171.20  
  Purchase #7 $169.66   3.299%   $175.2571   $175.26   $175.25   $175.30  
  7 purchase totals = $993.59       $1,091.9011   $1,091.91   $1,091.85   $1,092.00