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 $60.40   11.310%   $67.2312   $67.23   $67.25   $67.20  
  Purchase #2 $218.79   12.407%   $245.9353   $245.94   $245.95   $245.90  
  Purchase #3 $115.38   10.382%   $127.3588   $127.36   $127.35   $127.40  
  Purchase #4 $66.45   11.726%   $74.2419   $74.24   $74.25   $74.20  
  Purchase #5 $16.97   7.747%   $18.2847   $18.28   $18.30   $18.30  
  Purchase #6 $181.30   11.214%   $201.631   $201.63   $201.65   $201.60  
  Purchase #7 $51.45   9.596%   $56.3871   $56.39   $56.40   $56.40  
  7 purchase totals = $710.74       $791.0700   $791.07   $791.15   $791.00