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 $207.45   5.184%   $218.2042   $218.20   $218.20   $218.20  
  Purchase #2 $98.43   6.312%   $104.6429   $104.64   $104.65   $104.60  
  Purchase #3 $51.45   6.838%   $54.9682   $54.97   $54.95   $55.00  
  Purchase #4 $128.50   7.705%   $138.4009   $138.40   $138.40   $138.40  
  Purchase #5 $47.91   6.328%   $50.9417   $50.94   $50.95   $50.90  
  Purchase #6 $26.44   8.407%   $28.6628   $28.66   $28.65   $28.70  
  Purchase #7 $187.38   4.184%   $195.22   $195.22   $195.20   $195.20  
  7 purchase totals = $747.56       $791.0407   $791.03   $791.00   $791.00