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 $60.65   7.105%   $64.9592   $64.96   $64.95   $65.00  
  Purchase #2 $58.57   4.139%   $60.9942   $60.99   $61.00   $61.00  
  Purchase #3 $78.59   8.676%   $85.4085   $85.41   $85.40   $85.40  
  Purchase #4 $35.25   8.795%   $38.3502   $38.35   $38.35   $38.40  
  Purchase #5 $135.28   13.135%   $153.049   $153.05   $153.05   $153.00  
  Purchase #6 $59.35   7.137%   $63.5858   $63.59   $63.60   $63.60  
  Purchase #7 $242.53   13.387%   $274.9975   $275.00   $275.00   $275.00  
  7 purchase totals = $670.22       $741.3444   $741.35   $741.35   $741.40