Estava tendo problemas para importar o arquivo Notas.csv e o erro está na formatação nos campos de data e o numérico ao utilizar virgula em vez de ponto. Também está trocada a ordem que professor colocou. Corrigi o arquivo e espero que seja útil.
NUMERO,DATA_VENDA,CPF,MATRICULA,IMPOSTO
100,2015-01-01,7771579779,235,0.1
101,2015-01-01,50534475787,237,0.12
102,2015-01-01,8502682733,236,0.12
103,2015-01-01,5840119709,235,0.12
104,2015-01-01,1471156710,235,0.12
105,2015-01-01,94387575700,236,0.1
106,2015-01-01,3623344710,237,0.1
107,2015-01-01,5576228758,236,0.1
108,2015-01-01,19290992743,237,0.12
109,2015-01-01,94387575700,236,0.12
110,2015-01-01,5840119709,235,0.12
111,2015-01-01,492472718,237,0.1
112,2015-01-01,5840119709,236,0.12
113,2015-01-01,50534475787,235,0.1
114,2015-01-01,94387575700,235,0.1
115,2015-01-01,94387575700,236,0.12
116,2015-01-01,50534475787,235,0.1
117,2015-01-01,8719655770,236,0.12
118,2015-01-01,2600586709,235,0.12
119,2015-01-01,3623344710,236,0.1
120,2015-01-01,3623344710,235,0.1
121,2015-01-01,3623344710,235,0.12
122,2015-01-01,5648641702,237,0.1
123,2015-01-01,50534475787,237,0.12
124,2015-01-01,94387575700,235,0.12
125,2015-01-01,5840119709,237,0.12
126,2015-01-01,7771579779,237,0.12
127,2015-01-01,8502682733,236,0.12
128,2015-01-01,5648641702,237,0.12
129,2015-01-01,5840119709,237,0.12
130,2015-01-01,5576228758,236,0.12
131,2015-01-01,5840119709,236,0.12
132,2015-01-01,5576228758,236,0.1
133,2015-01-01,5576228758,235,0.12
134,2015-01-01,1471156710,235,0.12
135,2015-01-01,5648641702,235,0.12
136,2015-01-01,50534475787,236,0.1
137,2015-01-01,19290992743,237,0.12
138,2015-01-01,5648641702,235,0.1
139,2015-01-01,50534475787,236,0.1
140,2015-01-01,2600586709,237,0.12
141,2015-01-01,8502682733,237,0.1
142,2015-01-01,3623344710,236,0.1
143,2015-01-01,8719655770,236,0.12
144,2015-01-01,50534475787,236,0.12
145,2015-01-01,19290992743,235,0.1
146,2015-01-01,5648641702,236,0.12
147,2015-01-01,492472718,236,0.12
148,2015-01-01,492472718,236,0.1
149,2015-01-01,94387575700,235,0.12
150,2015-01-01,9283760794,236,0.12
151,2015-01-01,8719655770,235,0.1
152,2015-01-01,19290992743,237,0.1
153,2015-01-01,5576228758,237,0.12
154,2015-01-01,50534475787,237,0.1
155,2015-01-01,8502682733,237,0.1
156,2015-01-01,2600586709,237,0.1
157,2015-01-01,94387575700,235,0.1
158,2015-01-01,5840119709,236,0.1
159,2015-01-01,7771579779,237,0.12
160,2015-01-01,2600586709,236,0.1
161,2015-01-01,5576228758,235,0.1
162,2015-01-01,5840119709,235,0.12
163,2015-01-01,7771579779,235,0.1
164,2015-01-01,8502682733,235,0.1
165,2015-01-01,1471156710,235,0.1
166,2015-01-01,8502682733,237,0.1
167,2015-01-01,5576228758,235,0.1
168,2015-01-01,5576228758,235,0.1
169,2015-01-01,5840119709,237,0.12
170,2015-01-01,5840119709,237,0.12