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 $240.85   11.671%   $268.9596   $268.96   $268.95   $269.00  
  Purchase #2 $69.32   10.480%   $76.5847   $76.58   $76.60   $76.60  
  Purchase #3 $208.68   8.562%   $226.5472   $226.55   $226.55   $226.50  
  Purchase #4 $153.90   3.162%   $158.7663   $158.77   $158.75   $158.80  
  Purchase #5 $52.49   10.551%   $58.0282   $58.03   $58.05   $58.00  
  Purchase #6 $179.51   10.285%   $197.9726   $197.97   $197.95   $198.00  
  Purchase #7 $163.59   6.753%   $174.6372   $174.64   $174.65   $174.60  
  7 purchase totals = $1,068.34       $1,161.4958   $1,161.50   $1,161.50   $1,161.50