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 $64.63   13.678%   $73.4701   $73.47   $73.45   $73.50  
  Purchase #2 $208.98   11.466%   $232.9416   $232.94   $232.95   $232.90  
  Purchase #3 $31.27   9.873%   $34.3573   $34.36   $34.35   $34.40  
  Purchase #4 $42.41   8.735%   $46.1145   $46.11   $46.10   $46.10  
  Purchase #5 $69.86   4.636%   $73.0987   $73.10   $73.10   $73.10  
  Purchase #6 $229.83   4.396%   $239.9333   $239.93   $239.95   $239.90  
  Purchase #7 $164.62   7.561%   $177.0669   $177.07   $177.05   $177.10  
  7 purchase totals = $811.60       $876.9824   $876.98   $876.95   $877.00