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 $197.38   13.528%   $224.0816   $224.08   $224.10   $224.10  
  Purchase #2 $90.58   8.380%   $98.1706   $98.17   $98.15   $98.20  
  Purchase #3 $178.74   5.574%   $188.703   $188.70   $188.70   $188.70  
  Purchase #4 $56.68   10.459%   $62.6082   $62.61   $62.60   $62.60  
  Purchase #5 $9.31   6.183%   $9.8856   $9.89   $9.90   $9.90  
  Purchase #6 $73.47   5.771%   $77.71   $77.71   $77.70   $77.70  
  Purchase #7 $78.86   9.389%   $86.2642   $86.26   $86.25   $86.30  
  7 purchase totals = $685.02       $747.4232   $747.42   $747.40   $747.50