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 $203.44   5.226%   $214.0718   $214.07   $214.05   $214.10  
  Purchase #2 $65.67   4.663%   $68.7322   $68.73   $68.75   $68.70  
  Purchase #3 $77.68   4.614%   $81.2642   $81.26   $81.25   $81.30  
  Purchase #4 $86.55   13.117%   $97.9028   $97.90   $97.90   $97.90  
  Purchase #5 $209.30   3.174%   $215.9432   $215.94   $215.95   $215.90  
  Purchase #6 $239.88   4.416%   $250.4731   $250.47   $250.45   $250.50  
  Purchase #7 $13.51   7.341%   $14.5018   $14.50   $14.50   $14.50  
  7 purchase totals = $896.03       $942.8891   $942.87   $942.85   $942.90