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 $236.93   5.396%   $249.7147   $249.71   $249.70   $249.70  
  Purchase #2 $38.54   11.540%   $42.9875   $42.99   $43.00   $43.00  
  Purchase #3 $116.35   8.581%   $126.334   $126.33   $126.35   $126.30  
  Purchase #4 $31.90   4.618%   $33.3731   $33.37   $33.35   $33.40  
  Purchase #5 $244.89   13.709%   $278.462   $278.46   $278.45   $278.50  
  Purchase #6 $52.25   7.670%   $56.2576   $56.26   $56.25   $56.30  
  Purchase #7 $189.89   4.721%   $198.8547   $198.85   $198.85   $198.90  
  7 purchase totals = $910.75       $985.9836   $985.97   $985.95   $986.10