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 $14.71   10.422%   $16.2431   $16.24   $16.25   $16.20  
  Purchase #2 $144.43   4.666%   $151.1691   $151.17   $151.15   $151.20  
  Purchase #3 $11.85   12.847%   $13.3724   $13.37   $13.35   $13.40  
  Purchase #4 $146.54   9.868%   $161.0006   $161.00   $161.00   $161.00  
  Purchase #5 $250.76   9.476%   $274.522   $274.52   $274.50   $274.50  
  Purchase #6 $78.55   9.423%   $85.9518   $85.95   $85.95   $86.00  
  Purchase #7 $234.30   7.709%   $252.3622   $252.36   $252.35   $252.40  
  7 purchase totals = $881.14       $954.6212   $954.61   $954.55   $954.70