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 $104.99   13.622%   $119.2917   $119.29   $119.30   $119.30  
  Purchase #2 $127.96   10.435%   $141.3126   $141.31   $141.30   $141.30  
  Purchase #3 $40.88   4.131%   $42.5688   $42.57   $42.55   $42.60  
  Purchase #4 $73.74   3.873%   $76.596   $76.60   $76.60   $76.60  
  Purchase #5 $36.57   5.826%   $38.7006   $38.70   $38.70   $38.70  
  Purchase #6 $169.78   8.198%   $183.6986   $183.70   $183.70   $183.70  
  Purchase #7 $43.81   13.332%   $49.6507   $49.65   $49.65   $49.70  
  7 purchase totals = $597.73       $651.8190   $651.82   $651.80   $651.90