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 $78.38   4.620%   $82.0012   $82.00   $82.00   $82.00  
  Purchase #2 $177.42   10.270%   $195.641   $195.64   $195.65   $195.60  
  Purchase #3 $38.45   11.210%   $42.7602   $42.76   $42.75   $42.80  
  Purchase #4 $119.66   9.706%   $131.2742   $131.27   $131.25   $131.30  
  Purchase #5 $242.60   4.183%   $252.748   $252.75   $252.75   $252.70  
  Purchase #6 $12.57   11.390%   $14.0017   $14.00   $14.00   $14.00  
  Purchase #7 $202.78   5.509%   $213.9512   $213.95   $213.95   $214.00  
  7 purchase totals = $871.86       $932.3775   $932.37   $932.35   $932.40