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 $90.72   5.247%   $95.4801   $95.48   $95.50   $95.50  
  Purchase #2 $21.60   4.110%   $22.4878   $22.49   $22.50   $22.50  
  Purchase #3 $41.28   13.574%   $46.8833   $46.88   $46.90   $46.90  
  Purchase #4 $247.91   5.523%   $261.6021   $261.60   $261.60   $261.60  
  Purchase #5 $177.71   11.571%   $198.2728   $198.27   $198.25   $198.30  
  Purchase #6 $162.58   12.365%   $182.683   $182.68   $182.70   $182.70  
  Purchase #7 $185.42   9.382%   $202.8161   $202.82   $202.80   $202.80  
  7 purchase totals = $927.22       $1,010.2252   $1,010.22   $1,010.25   $1,010.30