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 $64.48   13.131%   $72.9469   $72.95   $72.95   $72.90  
  Purchase #2 $241.26   8.308%   $261.3039   $261.30   $261.30   $261.30  
  Purchase #3 $245.93   5.218%   $258.7626   $258.76   $258.75   $258.80  
  Purchase #4 $154.93   10.533%   $171.2488   $171.25   $171.25   $171.20  
  Purchase #5 $125.32   11.457%   $139.6779   $139.68   $139.70   $139.70  
  Purchase #6 $92.43   4.327%   $96.4294   $96.43   $96.45   $96.40  
  Purchase #7 $122.99   6.536%   $131.0286   $131.03   $131.05   $131.00  
  7 purchase totals = $1,047.34       $1,131.3981   $1,131.40   $1,131.45   $1,131.30