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 $47.67   12.262%   $53.5153   $53.52   $53.50   $53.50  
  Purchase #2 $41.65   8.493%   $45.1873   $45.19   $45.20   $45.20  
  Purchase #3 $88.87   4.109%   $92.5217   $92.52   $92.50   $92.50  
  Purchase #4 $180.99   9.193%   $197.6284   $197.63   $197.65   $197.60  
  Purchase #5 $73.75   11.812%   $82.4614   $82.46   $82.45   $82.50  
  Purchase #6 $240.49   3.551%   $249.0298   $249.03   $249.05   $249.00  
  Purchase #7 $146.85   11.581%   $163.8567   $163.86   $163.85   $163.90  
  7 purchase totals = $820.27       $884.2006   $884.21   $884.20   $884.20