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 $248.41   5.599%   $262.3185   $262.32   $262.30   $262.30  
  Purchase #2 $167.37   10.671%   $185.2301   $185.23   $185.25   $185.20  
  Purchase #3 $229.67   8.742%   $249.7478   $249.75   $249.75   $249.70  
  Purchase #4 $102.42   4.527%   $107.0566   $107.06   $107.05   $107.10  
  Purchase #5 $174.63   11.106%   $194.0244   $194.02   $194.00   $194.00  
  Purchase #6 $148.59   13.718%   $168.9736   $168.97   $168.95   $169.00  
  Purchase #7 $32.70   8.714%   $35.5495   $35.55   $35.55   $35.50  
  7 purchase totals = $1,103.79       $1,202.9005   $1,202.90   $1,202.85   $1,202.80