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 $44.93   9.248%   $49.0851   $49.09   $49.10   $49.10  
  Purchase #2 $180.47   7.131%   $193.3393   $193.34   $193.35   $193.30  
  Purchase #3 $156.71   8.446%   $169.9457   $169.95   $169.95   $169.90  
  Purchase #4 $92.99   11.703%   $103.8726   $103.87   $103.85   $103.90  
  Purchase #5 $76.46   12.675%   $86.1513   $86.15   $86.15   $86.20  
  Purchase #6 $56.32   8.584%   $61.1545   $61.15   $61.15   $61.20  
  Purchase #7 $62.44   12.690%   $70.3636   $70.36   $70.35   $70.40  
  7 purchase totals = $670.32       $733.9121   $733.91   $733.90   $734.00