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 $213.43   4.113%   $222.2084   $222.21   $222.20   $222.20  
  Purchase #2 $93.57   4.348%   $97.6384   $97.64   $97.65   $97.60  
  Purchase #3 $46.69   4.583%   $48.8298   $48.83   $48.85   $48.80  
  Purchase #4 $221.37   12.650%   $249.3733   $249.37   $249.35   $249.40  
  Purchase #5 $157.25   8.808%   $171.1006   $171.10   $171.10   $171.10  
  Purchase #6 $51.44   8.388%   $55.7548   $55.75   $55.75   $55.80  
  Purchase #7 $112.84   5.456%   $118.9966   $119.00   $119.00   $119.00  
  7 purchase totals = $896.59       $963.9019   $963.90   $963.90   $963.90