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 $25.70   3.811%   $26.6794   $26.68   $26.70   $26.70  
  Purchase #2 $208.69   7.147%   $223.6051   $223.61   $223.60   $223.60  
  Purchase #3 $116.36   9.675%   $127.6178   $127.62   $127.60   $127.60  
  Purchase #4 $68.43   5.697%   $72.3285   $72.33   $72.35   $72.30  
  Purchase #5 $183.73   11.748%   $205.3146   $205.31   $205.30   $205.30  
  Purchase #6 $224.55   6.815%   $239.8531   $239.85   $239.85   $239.90  
  Purchase #7 $155.36   9.163%   $169.5956   $169.60   $169.60   $169.60  
  7 purchase totals = $982.82       $1,064.9941   $1,065.00   $1,065.00   $1,065.00