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 $94.76   3.731%   $98.2955   $98.30   $98.30   $98.30  
  Purchase #2 $66.41   3.323%   $68.6168   $68.62   $68.60   $68.60  
  Purchase #3 $49.99   12.194%   $56.0858   $56.09   $56.10   $56.10  
  Purchase #4 $136.55   7.379%   $146.626   $146.63   $146.65   $146.60  
  Purchase #5 $159.67   6.640%   $170.2721   $170.27   $170.25   $170.30  
  Purchase #6 $124.61   12.696%   $140.4305   $140.43   $140.45   $140.40  
  Purchase #7 $214.52   11.286%   $238.7307   $238.73   $238.75   $238.70  
  7 purchase totals = $846.51       $919.0574   $919.07   $919.10   $919.00