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 $242.91   10.710%   $268.9257   $268.93   $268.95   $268.90  
  Purchase #2 $150.35   7.261%   $161.2669   $161.27   $161.25   $161.30  
  Purchase #3 $123.85   13.271%   $140.2861   $140.29   $140.30   $140.30  
  Purchase #4 $240.62   8.465%   $260.9885   $260.99   $261.00   $261.00  
  Purchase #5 $120.63   12.856%   $136.1382   $136.14   $136.15   $136.10  
  Purchase #6 $173.58   5.828%   $183.6962   $183.70   $183.70   $183.70  
  Purchase #7 $113.97   3.372%   $117.8131   $117.81   $117.80   $117.80  
  7 purchase totals = $1,165.91       $1,269.1147   $1,269.13   $1,269.15   $1,269.10