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 $68.63   11.600%   $76.5911   $76.59   $76.60   $76.60  
  Purchase #2 $44.25   4.728%   $46.3421   $46.34   $46.35   $46.30  
  Purchase #3 $127.86   8.767%   $139.0695   $139.07   $139.05   $139.10  
  Purchase #4 $76.65   4.292%   $79.9398   $79.94   $79.95   $79.90  
  Purchase #5 $35.35   7.823%   $38.1154   $38.12   $38.10   $38.10  
  Purchase #6 $208.83   3.579%   $216.304   $216.30   $216.30   $216.30  
  Purchase #7 $112.83   11.541%   $125.8517   $125.85   $125.85   $125.90  
  7 purchase totals = $674.40       $722.2136   $722.21   $722.20   $722.20