When using global variables, it is important to note that as variables are redefined within the cascade, this will in turn effect the value passed into the preceding variables.
$border-radius: 5px !default;
.block-01 {
border-radius: $border-radius;
}
.block-02 {
$border-radius: 10px;
border-radius: $border-radius;
}
.block-03 {
border-radius: $border-radius;
}