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 $61.91   12.454%   $69.6203   $69.62   $69.60   $69.60  
  Purchase #2 $146.76   12.194%   $164.6559   $164.66   $164.65   $164.70  
  Purchase #3 $124.83   7.484%   $134.1723   $134.17   $134.15   $134.20  
  Purchase #4 $49.68   13.566%   $56.4196   $56.42   $56.40   $56.40  
  Purchase #5 $237.45   7.624%   $255.5532   $255.55   $255.55   $255.60  
  Purchase #6 $190.71   4.543%   $199.374   $199.37   $199.35   $199.40  
  Purchase #7 $178.68   8.821%   $194.4414   $194.44   $194.45   $194.40  
  7 purchase totals = $990.02       $1,074.2367   $1,074.23   $1,074.15   $1,074.30