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 $68.94   10.608%   $76.2532   $76.25   $76.25   $76.30  
  Purchase #2 $143.94   7.646%   $154.9457   $154.95   $154.95   $154.90  
  Purchase #3 $68.79   6.579%   $73.3157   $73.32   $73.30   $73.30  
  Purchase #4 $102.66   7.549%   $110.4098   $110.41   $110.40   $110.40  
  Purchase #5 $53.69   10.763%   $59.4687   $59.47   $59.45   $59.50  
  Purchase #6 $208.76   10.807%   $231.3207   $231.32   $231.30   $231.30  
  Purchase #7 $91.68   8.289%   $99.2794   $99.28   $99.30   $99.30  
  7 purchase totals = $738.46       $804.9932   $805.00   $804.95   $805.00