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 $69.39   10.527%   $76.6947   $76.69   $76.70   $76.70  
  Purchase #2 $206.63   6.565%   $220.1953   $220.20   $220.20   $220.20  
  Purchase #3 $56.69   7.541%   $60.965   $60.97   $60.95   $61.00  
  Purchase #4 $101.69   5.580%   $107.3643   $107.36   $107.35   $107.40  
  Purchase #5 $59.26   7.406%   $63.6488   $63.65   $63.65   $63.60  
  Purchase #6 $165.74   6.833%   $177.065   $177.07   $177.05   $177.10  
  Purchase #7 $21.75   8.795%   $23.6629   $23.66   $23.65   $23.70  
  7 purchase totals = $681.15       $729.5960   $729.60   $729.55   $729.70