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 $168.90   10.124%   $185.9994   $186.00   $186.00   $186.00  
  Purchase #2 $143.33   6.161%   $152.1606   $152.16   $152.15   $152.20  
  Purchase #3 $6.95   13.262%   $7.8717   $7.87   $7.85   $7.90  
  Purchase #4 $247.48   9.646%   $271.3519   $271.35   $271.35   $271.40  
  Purchase #5 $207.66   13.105%   $234.8738   $234.87   $234.85   $234.90  
  Purchase #6 $69.80   13.843%   $79.4624   $79.46   $79.45   $79.50  
  Purchase #7 $52.82   3.375%   $54.6027   $54.60   $54.60   $54.60  
  7 purchase totals = $896.94       $986.3225   $986.31   $986.25   $986.50