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 $68.68   13.329%   $77.8344   $77.83   $77.85   $77.80  
  Purchase #2 $114.59   10.824%   $126.9932   $126.99   $127.00   $127.00  
  Purchase #3 $115.77   7.119%   $124.0117   $124.01   $124.00   $124.00  
  Purchase #4 $77.29   6.337%   $82.1879   $82.19   $82.20   $82.20  
  Purchase #5 $209.38   4.242%   $218.2619   $218.26   $218.25   $218.30  
  Purchase #6 $44.29   5.281%   $46.629   $46.63   $46.65   $46.60  
  Purchase #7 $64.65   8.416%   $70.0909   $70.09   $70.10   $70.10  
  7 purchase totals = $694.65       $746.0090   $746.00   $746.05   $746.00