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 $61.73   8.586%   $67.0301   $67.03   $67.05   $67.00  
  Purchase #2 $174.67   5.291%   $183.9118   $183.91   $183.90   $183.90  
  Purchase #3 $233.45   7.444%   $250.828   $250.83   $250.85   $250.80  
  Purchase #4 $175.79   3.664%   $182.2309   $182.23   $182.25   $182.20  
  Purchase #5 $236.25   8.593%   $256.551   $256.55   $256.55   $256.60  
  Purchase #6 $61.27   9.419%   $67.041   $67.04   $67.05   $67.00  
  Purchase #7 $190.71   4.476%   $199.2462   $199.25   $199.25   $199.20  
  7 purchase totals = $1,133.87       $1,206.8390   $1,206.84   $1,206.90   $1,206.70