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 $228.66   8.138%   $247.2684   $247.27   $247.25   $247.30  
  Purchase #2 $164.55   6.408%   $175.0944   $175.09   $175.10   $175.10  
  Purchase #3 $150.93   5.316%   $158.9534   $158.95   $158.95   $159.00  
  Purchase #4 $106.90   7.458%   $114.8726   $114.87   $114.85   $114.90  
  Purchase #5 $182.85   5.790%   $193.437   $193.44   $193.45   $193.40  
  Purchase #6 $79.41   9.393%   $86.869   $86.87   $86.85   $86.90  
  Purchase #7 $115.78   4.530%   $121.0248   $121.02   $121.00   $121.00  
  7 purchase totals = $1,029.08       $1,097.5196   $1,097.51   $1,097.45   $1,097.60