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 $60.76   8.705%   $66.0492   $66.05   $66.05   $66.00  
  Purchase #2 $117.94   8.668%   $128.163   $128.16   $128.15   $128.20  
  Purchase #3 $34.94   10.105%   $38.4707   $38.47   $38.45   $38.50  
  Purchase #4 $85.71   9.377%   $93.747   $93.75   $93.75   $93.70  
  Purchase #5 $147.94   13.696%   $168.2019   $168.20   $168.20   $168.20  
  Purchase #6 $197.59   12.398%   $222.0872   $222.09   $222.10   $222.10  
  Purchase #7 $229.43   5.495%   $242.0372   $242.04   $242.05   $242.00  
  7 purchase totals = $874.31       $958.7562   $958.76   $958.75   $958.70