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 $156.81   13.298%   $177.6626   $177.66   $177.65   $177.70  
  Purchase #2 $200.80   7.137%   $215.1311   $215.13   $215.15   $215.10  
  Purchase #3 $86.76   13.480%   $98.4552   $98.46   $98.45   $98.50  
  Purchase #4 $238.45   10.114%   $262.5668   $262.57   $262.55   $262.60  
  Purchase #5 $136.30   8.579%   $147.9932   $147.99   $148.00   $148.00  
  Purchase #6 $5.57   11.384%   $6.2041   $6.20   $6.20   $6.20  
  Purchase #7 $46.70   8.789%   $50.8045   $50.80   $50.80   $50.80  
  7 purchase totals = $871.39       $958.8175   $958.81   $958.80   $958.90