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 $46.59   4.214%   $48.5533   $48.55   $48.55   $48.60  
  Purchase #2 $185.25   7.354%   $198.8733   $198.87   $198.85   $198.90  
  Purchase #3 $124.65   13.735%   $141.7707   $141.77   $141.75   $141.80  
  Purchase #4 $217.41   8.271%   $235.392   $235.39   $235.40   $235.40  
  Purchase #5 $199.86   5.683%   $211.218   $211.22   $211.20   $211.20  
  Purchase #6 $199.68   11.632%   $222.9068   $222.91   $222.90   $222.90  
  Purchase #7 $145.57   12.624%   $163.9468   $163.95   $163.95   $163.90  
  7 purchase totals = $1,119.01       $1,222.6609   $1,222.66   $1,222.60   $1,222.70