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 $52.26   4.138%   $54.4225   $54.42   $54.40   $54.40  
  Purchase #2 $216.87   11.757%   $242.3674   $242.37   $242.35   $242.40  
  Purchase #3 $112.79   8.577%   $122.464   $122.46   $122.45   $122.50  
  Purchase #4 $58.88   5.652%   $62.2079   $62.21   $62.20   $62.20  
  Purchase #5 $189.49   11.701%   $211.6622   $211.66   $211.65   $211.70  
  Purchase #6 $79.54   8.309%   $86.149   $86.15   $86.15   $86.10  
  Purchase #7 $179.87   3.662%   $186.4568   $186.46   $186.45   $186.50  
  7 purchase totals = $889.70       $965.7298   $965.73   $965.65   $965.80