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 $209.48   11.123%   $232.7805   $232.78   $232.80   $232.80  
  Purchase #2 $226.72   9.689%   $248.6869   $248.69   $248.70   $248.70  
  Purchase #3 $243.49   7.734%   $262.3215   $262.32   $262.30   $262.30  
  Purchase #4 $169.77   7.507%   $182.5146   $182.51   $182.50   $182.50  
  Purchase #5 $103.81   9.348%   $113.5142   $113.51   $113.50   $113.50  
  Purchase #6 $70.90   11.382%   $78.9698   $78.97   $78.95   $79.00  
  Purchase #7 $83.76   13.680%   $95.2184   $95.22   $95.20   $95.20  
  7 purchase totals = $1,107.93       $1,214.0059   $1,214.00   $1,213.95   $1,214.00