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 $237.79   13.185%   $269.1426   $269.14   $269.15   $269.10  
  Purchase #2 $189.59   9.111%   $206.8635   $206.86   $206.85   $206.90  
  Purchase #3 $53.44   4.478%   $55.833   $55.83   $55.85   $55.80  
  Purchase #4 $38.74   10.851%   $42.9437   $42.94   $42.95   $42.90  
  Purchase #5 $9.90   11.789%   $11.0671   $11.07   $11.05   $11.10  
  Purchase #6 $16.95   4.159%   $17.655   $17.66   $17.65   $17.70  
  Purchase #7 $177.49   4.227%   $184.9925   $184.99   $185.00   $185.00  
  7 purchase totals = $723.90       $788.4974   $788.49   $788.50   $788.50