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 $65.44   11.825%   $73.1783   $73.18   $73.20   $73.20  
  Purchase #2 $42.36   10.560%   $46.8332   $46.83   $46.85   $46.80  
  Purchase #3 $215.89   8.159%   $233.5045   $233.50   $233.50   $233.50  
  Purchase #4 $55.69   3.117%   $57.4259   $57.43   $57.45   $57.40  
  Purchase #5 $23.68   11.855%   $26.4873   $26.49   $26.50   $26.50  
  Purchase #6 $26.46   7.345%   $28.4035   $28.40   $28.40   $28.40  
  Purchase #7 $76.35   12.802%   $86.1243   $86.12   $86.10   $86.10  
  7 purchase totals = $505.87       $551.9570   $551.95   $552.00   $551.90