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 $119.85   11.621%   $133.7778   $133.78   $133.80   $133.80  
  Purchase #2 $88.89   5.215%   $93.5256   $93.53   $93.55   $93.50  
  Purchase #3 $14.71   3.601%   $15.2397   $15.24   $15.25   $15.20  
  Purchase #4 $117.79   5.607%   $124.3945   $124.39   $124.40   $124.40  
  Purchase #5 $143.85   5.157%   $151.2683   $151.27   $151.25   $151.30  
  Purchase #6 $208.95   6.223%   $221.953   $221.95   $221.95   $222.00  
  Purchase #7 $250.67   13.469%   $284.4327   $284.43   $284.45   $284.40  
  7 purchase totals = $944.71       $1,024.5916   $1,024.59   $1,024.65   $1,024.60