Answer
Dependent upon the place to which a number is being rounded (tens, hundreds, tenths, hundredths, etc), the last digit determines which way a number is rounded. If the given digit is $\geq5$ then the number is rounded upwards in the next place (ie. 15,000 to 20,000). If the given digit is $\leq4$ then the number is rounded downwards in the next place (ie. 14,000 to 10,000).
Work Step by Step
1. 15,000 to 20,000 (rounding to the nearest ten-thousand).
a. note which digit represents the ten-thousand place
b. check if the immediate digit to the right is 5 or greater
c. increase the ten-thousand digit by one and make all subsequent numbers 0
2. 14,000 to 10,000 (rounding to the nearest ten-thousand).
a. note which digit represents the ten-thousand place
b. check if the immediate digit to the right is 4 or less
c. decrease the ten-thousand digit by one and make all subsequent numbers 0
