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 $48.83   6.545%   $52.0259   $52.03   $52.05   $52.00  
  Purchase #2 $197.64   10.273%   $217.9436   $217.94   $217.95   $217.90  
  Purchase #3 $73.44   11.321%   $81.7541   $81.75   $81.75   $81.80  
  Purchase #4 $80.77   6.852%   $86.3044   $86.30   $86.30   $86.30  
  Purchase #5 $103.72   11.751%   $115.9081   $115.91   $115.90   $115.90  
  Purchase #6 $244.58   4.704%   $256.085   $256.09   $256.10   $256.10  
  Purchase #7 $149.37   10.293%   $164.7447   $164.74   $164.75   $164.70  
  7 purchase totals = $898.35       $974.7658   $974.76   $974.80   $974.70