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 $192.49   13.306%   $218.1027   $218.10   $218.10   $218.10  
  Purchase #2 $242.62   12.770%   $273.6026   $273.60   $273.60   $273.60  
  Purchase #3 $219.29   4.794%   $229.8028   $229.80   $229.80   $229.80  
  Purchase #4 $69.49   8.520%   $75.4105   $75.41   $75.40   $75.40  
  Purchase #5 $218.91   10.369%   $241.6088   $241.61   $241.60   $241.60  
  Purchase #6 $248.27   9.346%   $271.4733   $271.47   $271.45   $271.50  
  Purchase #7 $60.39   3.124%   $62.2766   $62.28   $62.30   $62.30  
  7 purchase totals = $1,251.46       $1,372.2773   $1,372.27   $1,372.25   $1,372.30