It is quite easy to solve your task. You should create and use a new variable for summing values of the "Doctor Payment" column.
In your case the variable can be declared like this:
<variable name="total" class="java.lang.Integer" calculation="Sum">
<variableExpression><![CDATA[$F{payment}]]></variableExpression>
</variable>
The working example.
CSV datasource:
doctor_id,payment A1,123 B1,223 C2,234 D3,678 D1,343
The template:
<?xml version="1.0" encoding="UTF-8"?>
<jasperReport ...>
<queryString>
<![CDATA[]]>
</queryString>
<field name="doctor_id" class="java.lang.String"/>
<field name="payment" class="java.lang.Integer"/>
<variable name="total" class="java.lang.Integer" calculation="Sum">
<variableExpression><![CDATA[$F{payment}]]></variableExpression>
</variable>
<columnHeader>
<band height="20" splitType="Stretch">
<staticText>
<reportElement x="0" y="0" width="100" height="20"/>
<box leftPadding="10"/>
<textElement textAlignment="Center" verticalAlignment="Middle">
<font size="10" isBold="true" isItalic="true"/>
</textElement>
<text><![CDATA[Doctor ID]]></text>
</staticText>
<staticText>
<reportElement x="100" y="0" width="100" height="20"/>
<box leftPadding="10"/>
<textElement textAlignment="Center" verticalAlignment="Middle">
<font size="10" isBold="true" isItalic="true"/>
</textElement>
<text><![CDATA[Doctor Payment]]></text>
</staticText>
</band>
</columnHeader>
<detail>
<band height="20" splitType="Stretch">
<textField>
<reportElement x="0" y="0" width="100" height="20"/>
<box leftPadding="10"/>
<textElement/>
<textFieldExpression><![CDATA[$F{doctor_id}]]></textFieldExpression>
</textField>
<textField>
<reportElement x="100" y="0" width="100" height="20"/>
<box leftPadding="10"/>
<textElement/>
<textFieldExpression><![CDATA[$F{payment}]]></textFieldExpression>
</textField>
</band>
</detail>
<summary>
<band height="20">
<staticText>
<reportElement x="0" y="0" width="100" height="20"/>
<box leftPadding="10"/>
<textElement>
<font isBold="true"/>
</textElement>
<text><![CDATA[Total]]></text>
</staticText>
<textField>
<reportElement x="100" y="0" width="100" height="20"/>
<box leftPadding="10"/>
<textElement>
<font isBold="true" isItalic="true"/>
</textElement>
<textFieldExpression><![CDATA[$V{total}]]></textFieldExpression>
</textField>
</band>
</summary>
</jasperReport>
The result will be:
You can find a lot of info in the JasperReports Ultimate Guide.