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 $232.37   12.593%   $261.6324   $261.63   $261.65   $261.60  
  Purchase #2 $125.75   11.523%   $140.2402   $140.24   $140.25   $140.20  
  Purchase #3 $72.47   3.776%   $75.2065   $75.21   $75.20   $75.20  
  Purchase #4 $150.66   12.743%   $169.8586   $169.86   $169.85   $169.90  
  Purchase #5 $93.33   3.662%   $96.7477   $96.75   $96.75   $96.70  
  Purchase #6 $86.75   7.247%   $93.0368   $93.04   $93.05   $93.00  
  Purchase #7 $221.77   12.235%   $248.9036   $248.90   $248.90   $248.90  
  7 purchase totals = $983.10       $1,085.6258   $1,085.63   $1,085.65   $1,085.50