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 $49.93   5.271%   $52.5618   $52.56   $52.55   $52.60  
  Purchase #2 $189.26   5.450%   $199.5747   $199.57   $199.55   $199.60  
  Purchase #3 $155.52   13.414%   $176.3815   $176.38   $176.40   $176.40  
  Purchase #4 $54.73   11.407%   $60.9731   $60.97   $60.95   $61.00  
  Purchase #5 $119.99   11.577%   $133.8812   $133.88   $133.90   $133.90  
  Purchase #6 $199.42   8.358%   $216.0875   $216.09   $216.10   $216.10  
  Purchase #7 $55.79   4.720%   $58.4233   $58.42   $58.40   $58.40  
  7 purchase totals = $824.64       $897.8831   $897.87   $897.85   $898.00