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 $209.52   12.391%   $235.4816   $235.48   $235.50   $235.50  
  Purchase #2 $68.65   11.777%   $76.7349   $76.73   $76.75   $76.70  
  Purchase #3 $53.71   5.168%   $56.4857   $56.49   $56.50   $56.50  
  Purchase #4 $115.98   3.109%   $119.5858   $119.59   $119.60   $119.60  
  Purchase #5 $125.59   13.665%   $142.7519   $142.75   $142.75   $142.80  
  Purchase #6 $196.69   5.121%   $206.7625   $206.76   $206.75   $206.80  
  Purchase #7 $179.87   5.668%   $190.065   $190.07   $190.05   $190.10  
  7 purchase totals = $950.01       $1,027.8674   $1,027.87   $1,027.90   $1,028.00