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 $68.61   11.500%   $76.5002   $76.50   $76.50   $76.50  
  Purchase #2 $34.29   12.173%   $38.4641   $38.46   $38.45   $38.50  
  Purchase #3 $95.61   13.586%   $108.5996   $108.60   $108.60   $108.60  
  Purchase #4 $10.76   10.189%   $11.8563   $11.86   $11.85   $11.90  
  Purchase #5 $185.29   4.297%   $193.2519   $193.25   $193.25   $193.30  
  Purchase #6 $28.71   12.438%   $32.2809   $32.28   $32.30   $32.30  
  Purchase #7 $205.68   5.254%   $216.4864   $216.49   $216.50   $216.50  
  7 purchase totals = $628.95       $677.4394   $677.44   $677.45   $677.60