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 $59.49   6.129%   $63.1361   $63.14   $63.15   $63.10  
  Purchase #2 $247.32   12.493%   $278.2177   $278.22   $278.20   $278.20  
  Purchase #3 $11.85   9.360%   $12.9592   $12.96   $12.95   $13.00  
  Purchase #4 $16.58   10.279%   $18.2843   $18.28   $18.30   $18.30  
  Purchase #5 $41.63   13.292%   $47.1635   $47.16   $47.15   $47.20  
  Purchase #6 $46.68   4.244%   $48.6611   $48.66   $48.65   $48.70  
  Purchase #7 $199.96   7.125%   $214.2072   $214.21   $214.20   $214.20  
  7 purchase totals = $623.51       $682.6291   $682.63   $682.60   $682.70