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 $196.40   11.342%   $218.6757   $218.68   $218.70   $218.70  
  Purchase #2 $21.58   10.563%   $23.8595   $23.86   $23.85   $23.90  
  Purchase #3 $45.99   7.488%   $49.4337   $49.43   $49.45   $49.40  
  Purchase #4 $38.48   11.631%   $42.9556   $42.96   $42.95   $43.00  
  Purchase #5 $72.85   4.692%   $76.2681   $76.27   $76.25   $76.30  
  Purchase #6 $48.42   6.615%   $51.623   $51.62   $51.60   $51.60  
  Purchase #7 $53.46   4.869%   $56.063   $56.06   $56.05   $56.10  
  7 purchase totals = $477.18       $518.8786   $518.88   $518.85   $519.00