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 $208.54   11.201%   $231.8986   $231.90   $231.90   $231.90  
  Purchase #2 $190.90   11.688%   $213.2124   $213.21   $213.20   $213.20  
  Purchase #3 $152.94   5.610%   $161.5199   $161.52   $161.50   $161.50  
  Purchase #4 $224.95   12.569%   $253.224   $253.22   $253.20   $253.20  
  Purchase #5 $67.80   12.592%   $76.3374   $76.34   $76.35   $76.30  
  Purchase #6 $156.63   4.759%   $164.084   $164.08   $164.10   $164.10  
  Purchase #7 $177.89   10.234%   $196.0953   $196.10   $196.10   $196.10  
  7 purchase totals = $1,179.65       $1,296.3716   $1,296.37   $1,296.35   $1,296.30