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 $114.52   11.304%   $127.4653   $127.47   $127.45   $127.50  
  Purchase #2 $84.41   9.118%   $92.1065   $92.11   $92.10   $92.10  
  Purchase #3 $121.96   9.801%   $133.9133   $133.91   $133.90   $133.90  
  Purchase #4 $188.57   5.846%   $199.5938   $199.59   $199.60   $199.60  
  Purchase #5 $46.73   3.538%   $48.3833   $48.38   $48.40   $48.40  
  Purchase #6 $119.53   9.241%   $130.5758   $130.58   $130.60   $130.60  
  Purchase #7 $226.97   11.272%   $252.5541   $252.55   $252.55   $252.60  
  7 purchase totals = $902.69       $984.5921   $984.59   $984.60   $984.70