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 $60.42   6.540%   $64.3715   $64.37   $64.35   $64.40  
  Purchase #2 $237.97   12.429%   $267.5473   $267.55   $267.55   $267.50  
  Purchase #3 $75.46   11.630%   $84.236   $84.24   $84.25   $84.20  
  Purchase #4 $208.55   8.189%   $225.6282   $225.63   $225.65   $225.60  
  Purchase #5 $169.43   8.244%   $183.3978   $183.40   $183.40   $183.40  
  Purchase #6 $159.35   11.829%   $178.1995   $178.20   $178.20   $178.20  
  Purchase #7 $157.41   4.221%   $164.0543   $164.05   $164.05   $164.10  
  7 purchase totals = $1,068.59       $1,167.4346   $1,167.44   $1,167.45   $1,167.40