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 $248.50   10.339%   $274.1924   $274.19   $274.20   $274.20  
  Purchase #2 $168.57   8.382%   $182.6995   $182.70   $182.70   $182.70  
  Purchase #3 $66.66   6.720%   $71.1396   $71.14   $71.15   $71.10  
  Purchase #4 $99.25   5.376%   $104.5857   $104.59   $104.60   $104.60  
  Purchase #5 $231.51   12.124%   $259.5783   $259.58   $259.60   $259.60  
  Purchase #6 $132.62   11.129%   $147.3793   $147.38   $147.40   $147.40  
  Purchase #7 $183.66   6.503%   $195.6034   $195.60   $195.60   $195.60  
  7 purchase totals = $1,130.77       $1,235.1782   $1,235.18   $1,235.25   $1,235.20