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 $167.61   9.577%   $183.662   $183.66   $183.65   $183.70  
  Purchase #2 $141.83   5.794%   $150.0476   $150.05   $150.05   $150.00  
  Purchase #3 $236.71   11.314%   $263.4914   $263.49   $263.50   $263.50  
  Purchase #4 $158.52   11.792%   $177.2127   $177.21   $177.20   $177.20  
  Purchase #5 $33.38   3.325%   $34.4899   $34.49   $34.50   $34.50  
  Purchase #6 $119.91   4.189%   $124.933   $124.93   $124.95   $124.90  
  Purchase #7 $245.25   12.181%   $275.1239   $275.12   $275.10   $275.10  
  7 purchase totals = $1,103.21       $1,208.9605   $1,208.95   $1,208.95   $1,208.90