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 $55.51   10.699%   $61.449   $61.45   $61.45   $61.40  
  Purchase #2 $234.34   13.471%   $265.9079   $265.91   $265.90   $265.90  
  Purchase #3 $244.81   4.811%   $256.5878   $256.59   $256.60   $256.60  
  Purchase #4 $200.97   12.244%   $225.5768   $225.58   $225.60   $225.60  
  Purchase #5 $51.76   9.608%   $56.7331   $56.73   $56.75   $56.70  
  Purchase #6 $140.41   12.119%   $157.4263   $157.43   $157.45   $157.40  
  Purchase #7 $239.72   13.617%   $272.3627   $272.36   $272.35   $272.40  
  7 purchase totals = $1,167.52       $1,296.0436   $1,296.05   $1,296.10   $1,296.00