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 $67.92   13.604%   $77.1598   $77.16   $77.15   $77.20  
  Purchase #2 $192.95   8.187%   $208.7468   $208.75   $208.75   $208.70  
  Purchase #3 $221.65   9.141%   $241.911   $241.91   $241.90   $241.90  
  Purchase #4 $179.54   3.303%   $185.4702   $185.47   $185.45   $185.50  
  Purchase #5 $5.87   7.830%   $6.3296   $6.33   $6.35   $6.30  
  Purchase #6 $123.57   7.630%   $132.9984   $133.00   $133.00   $133.00  
  Purchase #7 $245.97   6.725%   $262.5115   $262.51   $262.50   $262.50  
  7 purchase totals = $1,037.47       $1,115.1273   $1,115.13   $1,115.10   $1,115.10