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 $206.93   13.452%   $234.7662   $234.77   $234.75   $234.80  
  Purchase #2 $8.79   7.547%   $9.4534   $9.45   $9.45   $9.50  
  Purchase #3 $146.44   11.587%   $163.408   $163.41   $163.40   $163.40  
  Purchase #4 $185.41   6.531%   $197.5191   $197.52   $197.50   $197.50  
  Purchase #5 $16.26   11.140%   $18.0714   $18.07   $18.05   $18.10  
  Purchase #6 $221.51   8.623%   $240.6108   $240.61   $240.60   $240.60  
  Purchase #7 $57.25   6.734%   $61.1052   $61.11   $61.10   $61.10  
  7 purchase totals = $842.59       $924.9341   $924.94   $924.85   $925.00