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 $238.38   9.636%   $261.3503   $261.35   $261.35   $261.40  
  Purchase #2 $36.31   13.160%   $41.0884   $41.09   $41.10   $41.10  
  Purchase #3 $154.74   9.479%   $169.4078   $169.41   $169.40   $169.40  
  Purchase #4 $126.48   6.535%   $134.7455   $134.75   $134.75   $134.70  
  Purchase #5 $214.75   6.851%   $229.4625   $229.46   $229.45   $229.50  
  Purchase #6 $94.43   12.537%   $106.2687   $106.27   $106.25   $106.30  
  Purchase #7 $134.59   4.704%   $140.9211   $140.92   $140.90   $140.90  
  7 purchase totals = $999.68       $1,083.2443   $1,083.25   $1,083.20   $1,083.30