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 $70.69   6.177%   $75.0565   $75.06   $75.05   $75.10  
  Purchase #2 $33.48   4.659%   $35.0398   $35.04   $35.05   $35.00  
  Purchase #3 $109.69   4.356%   $114.4681   $114.47   $114.45   $114.50  
  Purchase #4 $174.40   6.358%   $185.4884   $185.49   $185.50   $185.50  
  Purchase #5 $235.26   5.696%   $248.6604   $248.66   $248.65   $248.70  
  Purchase #6 $190.92   12.271%   $214.3478   $214.35   $214.35   $214.30  
  Purchase #7 $128.70   6.537%   $137.1131   $137.11   $137.10   $137.10  
  7 purchase totals = $943.14       $1,010.1741   $1,010.18   $1,010.15   $1,010.20