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 $61.83   5.234%   $65.0662   $65.07   $65.05   $65.10  
  Purchase #2 $14.94   12.647%   $16.8295   $16.83   $16.85   $16.80  
  Purchase #3 $163.68   11.748%   $182.9091   $182.91   $182.90   $182.90  
  Purchase #4 $154.37   9.722%   $169.3779   $169.38   $169.40   $169.40  
  Purchase #5 $155.45   3.863%   $161.455   $161.46   $161.45   $161.50  
  Purchase #6 $57.72   4.715%   $60.4415   $60.44   $60.45   $60.40  
  Purchase #7 $90.36   11.758%   $100.9845   $100.98   $101.00   $101.00  
  7 purchase totals = $698.35       $757.0637   $757.07   $757.10   $757.10