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 $249.93   5.727%   $264.2435   $264.24   $264.25   $264.20  
  Purchase #2 $78.42   5.715%   $82.9017   $82.90   $82.90   $82.90  
  Purchase #3 $105.60   7.551%   $113.5739   $113.57   $113.55   $113.60  
  Purchase #4 $191.76   3.568%   $198.602   $198.60   $198.60   $198.60  
  Purchase #5 $71.39   7.493%   $76.7393   $76.74   $76.75   $76.70  
  Purchase #6 $107.55   5.505%   $113.4706   $113.47   $113.45   $113.50  
  Purchase #7 $63.43   5.421%   $66.8685   $66.87   $66.85   $66.90  
  7 purchase totals = $868.08       $916.3995   $916.39   $916.35   $916.40