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 $245.83   4.125%   $255.9705   $255.97   $255.95   $256.00  
  Purchase #2 $247.80   4.858%   $259.8381   $259.84   $259.85   $259.80  
  Purchase #3 $25.77   3.601%   $26.698   $26.70   $26.70   $26.70  
  Purchase #4 $119.26   4.266%   $124.3476   $124.35   $124.35   $124.30  
  Purchase #5 $52.67   4.628%   $55.1076   $55.11   $55.10   $55.10  
  Purchase #6 $81.47   6.733%   $86.9554   $86.96   $86.95   $87.00  
  Purchase #7 $188.62   4.472%   $197.0551   $197.06   $197.05   $197.10  
  7 purchase totals = $961.42       $1,005.9723   $1,005.99   $1,005.95   $1,006.00