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 $85.63   10.662%   $94.7599   $94.76   $94.75   $94.80  
  Purchase #2 $43.98   12.105%   $49.3038   $49.30   $49.30   $49.30  
  Purchase #3 $183.42   9.375%   $200.6156   $200.62   $200.60   $200.60  
  Purchase #4 $189.61   11.650%   $211.6996   $211.70   $211.70   $211.70  
  Purchase #5 $30.40   10.792%   $33.6808   $33.68   $33.70   $33.70  
  Purchase #6 $26.74   3.322%   $27.6283   $27.63   $27.65   $27.60  
  Purchase #7 $28.49   13.715%   $32.3974   $32.40   $32.40   $32.40  
  7 purchase totals = $588.27       $650.0854   $650.09   $650.10   $650.10