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 $219.26   13.855%   $249.6385   $249.64   $249.65   $249.60  
  Purchase #2 $223.92   10.597%   $247.6488   $247.65   $247.65   $247.60  
  Purchase #3 $127.48   4.661%   $133.4218   $133.42   $133.40   $133.40  
  Purchase #4 $93.49   8.455%   $101.3946   $101.39   $101.40   $101.40  
  Purchase #5 $157.85   11.515%   $176.0264   $176.03   $176.05   $176.00  
  Purchase #6 $153.97   13.793%   $175.2071   $175.21   $175.20   $175.20  
  Purchase #7 $148.69   13.300%   $168.4658   $168.47   $168.45   $168.50  
  7 purchase totals = $1,124.66       $1,251.8030   $1,251.81   $1,251.80   $1,251.70