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 $172.38   12.566%   $194.0413   $194.04   $194.05   $194.00  
  Purchase #2 $168.67   9.528%   $184.7409   $184.74   $184.75   $184.70  
  Purchase #3 $73.89   3.789%   $76.6897   $76.69   $76.70   $76.70  
  Purchase #4 $86.45   10.660%   $95.6656   $95.67   $95.65   $95.70  
  Purchase #5 $20.65   4.808%   $21.6429   $21.64   $21.65   $21.60  
  Purchase #6 $227.93   13.838%   $259.471   $259.47   $259.45   $259.50  
  Purchase #7 $50.33   3.483%   $52.083   $52.08   $52.10   $52.10  
  7 purchase totals = $800.30       $884.3344   $884.33   $884.35   $884.30