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 $68.52   9.859%   $75.2754   $75.28   $75.30   $75.30  
  Purchase #2 $128.25   5.229%   $134.9562   $134.96   $134.95   $135.00  
  Purchase #3 $113.48   13.229%   $128.4923   $128.49   $128.50   $128.50  
  Purchase #4 $45.88   13.449%   $52.0504   $52.05   $52.05   $52.10  
  Purchase #5 $241.93   4.725%   $253.3612   $253.36   $253.35   $253.40  
  Purchase #6 $89.99   6.269%   $95.6315   $95.63   $95.65   $95.60  
  Purchase #7 $49.35   13.665%   $56.0937   $56.09   $56.10   $56.10  
  7 purchase totals = $737.40       $795.8607   $795.86   $795.90   $796.00