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 $215.95   11.256%   $240.2573   $240.26   $240.25   $240.30  
  Purchase #2 $249.48   4.503%   $260.7141   $260.71   $260.70   $260.70  
  Purchase #3 $185.25   8.800%   $201.552   $201.55   $201.55   $201.60  
  Purchase #4 $158.43   8.213%   $171.4419   $171.44   $171.45   $171.40  
  Purchase #5 $21.48   7.239%   $23.0349   $23.03   $23.05   $23.00  
  Purchase #6 $195.51   9.206%   $213.5087   $213.51   $213.50   $213.50  
  Purchase #7 $42.56   12.758%   $47.9898   $47.99   $48.00   $48.00  
  7 purchase totals = $1,068.66       $1,158.4987   $1,158.49   $1,158.50   $1,158.50