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 $134.41   4.738%   $140.7783   $140.78   $140.80   $140.80  
  Purchase #2 $164.88   7.497%   $177.2411   $177.24   $177.25   $177.20  
  Purchase #3 $124.72   8.518%   $135.3436   $135.34   $135.35   $135.30  
  Purchase #4 $35.48   12.716%   $39.9916   $39.99   $40.00   $40.00  
  Purchase #5 $100.39   3.317%   $103.7199   $103.72   $103.70   $103.70  
  Purchase #6 $240.65   10.400%   $265.6776   $265.68   $265.70   $265.70  
  Purchase #7 $81.92   8.833%   $89.156   $89.16   $89.15   $89.20  
  7 purchase totals = $882.45       $951.9081   $951.91   $951.95   $951.90