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 $58.45   11.310%   $65.0607   $65.06   $65.05   $65.10  
  Purchase #2 $227.82   13.682%   $258.9903   $258.99   $259.00   $259.00  
  Purchase #3 $129.48   10.350%   $142.8812   $142.88   $142.90   $142.90  
  Purchase #4 $248.57   12.238%   $278.99   $278.99   $279.00   $279.00  
  Purchase #5 $186.73   11.542%   $208.2824   $208.28   $208.30   $208.30  
  Purchase #6 $235.56   5.806%   $249.2366   $249.24   $249.25   $249.20  
  Purchase #7 $161.88   7.456%   $173.9498   $173.95   $173.95   $173.90  
  7 purchase totals = $1,248.49       $1,377.3910   $1,377.39   $1,377.45   $1,377.40