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 $55.97   13.675%   $63.6239   $63.62   $63.60   $63.60  
  Purchase #2 $185.67   3.558%   $192.2761   $192.28   $192.30   $192.30  
  Purchase #3 $46.46   13.352%   $52.6633   $52.66   $52.65   $52.70  
  Purchase #4 $234.77   3.180%   $242.2357   $242.24   $242.25   $242.20  
  Purchase #5 $97.71   11.578%   $109.0229   $109.02   $109.00   $109.00  
  Purchase #6 $36.57   4.103%   $38.0705   $38.07   $38.05   $38.10  
  Purchase #7 $208.69   10.469%   $230.5378   $230.54   $230.55   $230.50  
  7 purchase totals = $865.84       $928.4302   $928.43   $928.40   $928.40