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 $185.99   11.824%   $207.9815   $207.98   $208.00   $208.00  
  Purchase #2 $66.74   6.218%   $70.8899   $70.89   $70.90   $70.90  
  Purchase #3 $25.72   6.515%   $27.3957   $27.40   $27.40   $27.40  
  Purchase #4 $227.92   4.493%   $238.1604   $238.16   $238.15   $238.20  
  Purchase #5 $125.53   7.122%   $134.4702   $134.47   $134.45   $134.50  
  Purchase #6 $248.61   3.203%   $256.573   $256.57   $256.55   $256.60  
  Purchase #7 $239.33   12.689%   $269.6986   $269.70   $269.70   $269.70  
  7 purchase totals = $1,119.84       $1,205.1693   $1,205.17   $1,205.15   $1,205.30