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 $104.87   3.152%   $108.1755   $108.18   $108.20   $108.20  
  Purchase #2 $202.32   11.229%   $225.0385   $225.04   $225.05   $225.00  
  Purchase #3 $242.63   6.735%   $258.9711   $258.97   $258.95   $259.00  
  Purchase #4 $193.73   6.194%   $205.7296   $205.73   $205.75   $205.70  
  Purchase #5 $160.87   7.262%   $172.5524   $172.55   $172.55   $172.60  
  Purchase #6 $48.30   3.116%   $49.805   $49.81   $49.80   $49.80  
  Purchase #7 $182.50   7.668%   $196.4941   $196.49   $196.50   $196.50  
  7 purchase totals = $1,135.22       $1,216.7662   $1,216.77   $1,216.80   $1,216.80