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 $57.71   13.183%   $65.3179   $65.32   $65.30   $65.30  
  Purchase #2 $157.30   10.866%   $174.3922   $174.39   $174.40   $174.40  
  Purchase #3 $225.37   12.868%   $254.3706   $254.37   $254.35   $254.40  
  Purchase #4 $93.92   7.788%   $101.2345   $101.23   $101.25   $101.20  
  Purchase #5 $187.82   5.759%   $198.6366   $198.64   $198.65   $198.60  
  Purchase #6 $63.65   4.719%   $66.6536   $66.65   $66.65   $66.70  
  Purchase #7 $206.99   5.324%   $218.0101   $218.01   $218.00   $218.00  
  7 purchase totals = $992.76       $1,078.6155   $1,078.61   $1,078.60   $1,078.60