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 $202.88   12.679%   $228.6032   $228.60   $228.60   $228.60  
  Purchase #2 $127.26   9.787%   $139.7149   $139.71   $139.70   $139.70  
  Purchase #3 $119.33   11.417%   $132.9539   $132.95   $132.95   $133.00  
  Purchase #4 $214.35   10.850%   $237.607   $237.61   $237.60   $237.60  
  Purchase #5 $91.88   7.460%   $98.7342   $98.73   $98.75   $98.70  
  Purchase #6 $114.35   4.371%   $119.3482   $119.35   $119.35   $119.30  
  Purchase #7 $153.31   9.675%   $168.1427   $168.14   $168.15   $168.10  
  7 purchase totals = $1,023.36       $1,125.1041   $1,125.09   $1,125.10   $1,125.00