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 $61.79   3.556%   $63.9873   $63.99   $64.00   $64.00  
  Purchase #2 $163.70   5.462%   $172.6413   $172.64   $172.65   $172.60  
  Purchase #3 $207.65   9.272%   $226.9033   $226.90   $226.90   $226.90  
  Purchase #4 $86.59   11.316%   $96.3885   $96.39   $96.40   $96.40  
  Purchase #5 $200.44   3.807%   $208.0708   $208.07   $208.05   $208.10  
  Purchase #6 $26.29   5.317%   $27.6878   $27.69   $27.70   $27.70  
  Purchase #7 $171.60   9.104%   $187.2225   $187.22   $187.20   $187.20  
  7 purchase totals = $918.06       $982.9015   $982.90   $982.90   $982.90