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 $99.87   8.771%   $108.6296   $108.63   $108.65   $108.60  
  Purchase #2 $194.83   11.359%   $216.9607   $216.96   $216.95   $217.00  
  Purchase #3 $112.68   11.246%   $125.352   $125.35   $125.35   $125.40  
  Purchase #4 $168.34   5.116%   $176.9523   $176.95   $176.95   $177.00  
  Purchase #5 $82.31   13.161%   $93.1428   $93.14   $93.15   $93.10  
  Purchase #6 $45.88   8.717%   $49.8794   $49.88   $49.90   $49.90  
  Purchase #7 $239.31   9.115%   $261.1231   $261.12   $261.10   $261.10  
  7 purchase totals = $943.22       $1,032.0399   $1,032.03   $1,032.05   $1,032.10